A11A-0001 0800h
Hydrocarbon Measurements during the MCMA2003 Field Experiment: Intercomparison and Analysis
To better understand the photochemical production of ozone and secondary organic aerosol in Mexico City, volatile hydrocarbon measurements were made from the roof top of the Mexican National Research and Training Center (CENICA) in Iztapalapa during the Mexico City Metropolitan Area field experiment in April 2003. Three distinct techniques were used: on-line chemical ionization using a proton transfer reaction mass spectrometer (PTR-MS), long path measurements using a UV differential optical absorption spectrometer (DOAS), and gas chromatography - flame ionization analysis (GC-FID) of canisters samples. The PTR-MS provided high time resolution data of several aromatic and oxygenated species, and monitored masses corresponding to volatile aromatic oxidation products. The DOAS instrument likewise made high time resolution measurements of a several aromatic and oxygenated species, while the canister data reported C2-C10 hydrocarbons. An intercomparison of these techniques for several species measured in common is reported, including a comparison of standards used for calibration. Results show a good agreement between the PTR-MS and UV DOAS calibrations for several aromatic species. Differences in ambient data were therefore determined to be due to significant concentration gradients over the path length of the DOAS. The comparison between PTR-MS and GC-FID data indicate that fragmentation of higher aromatics likely caused the PTR to overestimate benzene mixing ratios. The ambient aromatic data displayed significant diel variability. Oxygenated species displayed different temporal variability patterns, indicating the importance of photochemical sources in the afternoon. These temporal patterns and hydrocarbon ratios were compared to those observed in US cities to highlight differences between Mexico City hydrocarbon distribution and reactivity.
A11A-0002 0800h
Measurements of Criteria Pollutants in Suburban Locations in the Mexico City Metropolitan Area
In the town of Santa Ana in the southern part of the Mexico City Metropolitan Area (MCMA) at an approximate height of 370 meters above the Valley of Mexico, a series of criteria pollutants (nitrogen dioxide, ozone, sulfur dioxide, and carbon monoxide) and meteorological parameters (wind speed and direction, temperature and relative humidity) were measured during the MCMA-2003 field campaign during April 2003. Santa Ana is considered a border site, agriculture being the predominant activity. The generated data in Santa Ana was compared with those from two representative atmospheric monitoring stations from the southeast zone (CENICA Supersite) and southwest (Revolucion Station) of Mexico City. The carbon monoxide and ozone concentrations measured in Santa Ana are atypical for a rural area. The sulfur dioxide and nitrogen dioxide concentrations are characteristic of the local activity. The average obtained during the measurement time for carbon monoxide was 0.86 ppm, the presence of the contaminant was within a 0.3 to 1.5 ppm range, 5 to 95 percentile, and does not follow the observed behavior of the monitoring stations that are located inside the urban area, although during the night (10 pm to 6 am) the carbon monoxide in Santa Ana was preset in levels from 0.4 to 1.5 ppm, 5 to 95 percentiles, average 0.92 ppm, above the reported concentrations at Revolucion Station, levels from 0.1 to 1.7 ppm, 5 to 95 percentiles; average 0.72 ppm. The presence of this contaminant can be attributed to transportation and accumulation phenomena. The ozone daytime behavior is similar to the one observed in the CENICA and Revolucion stations, but with a lower magnitude, the daily maximum generally occuring 2 or 3 hours after the urban stations. The one-hour average maximum values were 133 ppb in Santa Ana area and 188 ppb in the city. During the night the average concentrations were 37 ppb in Santa Ana and 17 ppb in the urban area. Nevertheless, the ozone average value in Santa Ana during the study was 49 ppb, slightly higher than the one obtained in the urban area, which was 44 ppb. The presence of this contaminant can be possibly attributed to the transportation and accumulation factors as well as to the low reactivity due to the absence of NOx, as explained in Dommen Josef and Prevät, S.H. Andre, 2002, Characterization of the photooxidant formation in the metropolitan area of Milan from aircraft measurements, Journal of Geophysical Research, 107 (D22): 8197, doi: 10.1029/2000JD000283.
A11A-0003 0800h
Open-path Emission Factors Derived from DOAS and FTIR Measurements in the Mexico City Metropolitan Area
Mobile sources are responsible for about 50% of VOC (volatile organic compounds) and about 70% of NOx emissions in the Mexico City Metropolitan Area (MCMA). A novel approach has been developed to derive emission factors for mobile sources that are representative of the overall vehicle fleet, using collocated open-path Differential Optical Absorption Spectroscopy (DOAS) and Fourier Transform Infrared (FTIR) spectroscopic measurements. Measurements were recorded at two sites within the MCMA: (1) research-grade DOAS and FTIR systems were operated at the Mexican National Research and Training Center (CENICA) in Iztapalapa, (2) a research grade FTIR was operated at La Merced. In addition, point-sampling with a proton transfer reaction mass spectrometer (PTR-MS) was performed on the same location and the calibration standards for the PTR-MS and the DOAS instruments were cross-calibrated. The DOAS measured speciated aromatic hydrocarbons, including benzene, toluene, m-xylene, p-xylene, ethylbenzene (and mono-substituted alkylbenzenes), benzaldehyde, phenol, and p-cresol. The DOAS detection of aromatic hydrocarbons in the UV/vis spectral range between 250 to 310 nm suffers from the interference of molecular oxygen, and a novel approach is being presented that enables measurement of absolute concentrations of the above species. Further, HONO, NO2, SO2 and HCHO were measured at longer wavelengths. In combination with FTIR measurements of CO, CO2, NO, HCHO, ethylene, ethene, and total alkane, average emission factors for NOx, SO2 and numerous hydrocarbons were derived and scaled with fuel sales data to estimate total emissions of the vehicle fleet in the MCMA. The advantages and limitations of this low-cost emission inventory for mobile sources are decsribed.
A11A-0004 0800h
Location and Mapping of an Ethyl Acetate Plume in Mexico City
A major goal of the 2003 Mexico City Metropolitan Area (MCMA) field campaign was to gain a better understanding of the dispersion and transport of volatile organic compounds (VOCs) in this urban airshed. Continuous monitoring of VOCs in the atmosphere and identification and quantification of their emission sources is complicated by two factors: first, there are hundreds of different VOC species released daily in the MCMA atmosphere, and second, few real time (1-10 second) measurement techniques have been available to provide the high resolution spatial and/or temporal data usually required to locate VOC emission sources and measure their flux strength. A relatively new technique, Proton Transfer Reaction Mass Spectometery (PTR-MS) provides this capability and was used to locate and quantify a significant source of ethyl acetate in the Iztapalapa region of Mexico City. Two PTR-MS systems were deployed during the 2003 MCMA campaign, the MSU PTR-MS was operated on-board the Aerodyne Mobile Laboratory while the PNNL instrument located on the roof at the National Center for Environmental Research and Training (Centro Nacional de Investigacion y Capacitacion Ambiental or CENICA). The uniqueness of the ethyl acetate signature allowed the MSU PTR-MS on-board the mobile lab to track the ethyl acetate plume back to its source. A short movie documenting the plume mapping and location of the source of the ethyl acetate emission will be shown. Knowing of the plume source location and the local meteorological conditions, the time resolved responses from the PNNL PTR-MS at the CENCIA location have been applied to a simple plume model to estimate the plume's emission flux strength.
A11A-0005 0800h
Exploratory Investigation of Concentrations of Total Gaseous Mercury in the Mexico City Metropolitan Area
Total Gaseous Mercury (TGM) in ambient air at several locations within Mexico Valley Metropolitan Area (Zona Metropolitana del Valle de Mexico, ZMVM, in Spanish) was measured during the Fall of 2002 and the first quarter of 2003. Among these locations were Tecamachalco (19°26'N; 99°13'W), San Agustin (19°31'N; 99°01'W), Xalostoc (19°31'N; 99°04'W) and Iztapalapa (19°21'N; 99°04'W). San Agustin and Xalostoc border the State of Mexico. Iztapalapa contains CENICA's monitoring station, and Mercury was one of the parameters measured here during the MCMA-2003 field campaign of the atmospheric chemistry taking place in ZMVM in April of 2003. This last site was used to monitor Mercury during three different seasons. The reported concentrations of Mercury vapor were measured continuously using cold vapor Atomic Fluorescence Spectroscopy (Tekran 2537A analyzer), with a detection limit of 0.10 ng m-3 and a monitoring frequency of five minutes. The average TGM concentrations reported were 13.42, 10.22, 8.46 and 34.2 ng m-3 for Iztapalapa in the months of September, October and November of 2002 and April of 2003 during the MCMA-2003 field campaign, respectively. For Tecamachalco, a concentration of 49.67 ng m-3 was reported in January, 11.3 ng m-3, for San Agustin in February and 31.99 ng m-3 for Xalostoc in March of 2003.The daily maximums, 24 hourly average, for the same periods are 223.5, 78.2, 31.4 and 503.75 ng m-3 for Iztapalapa, 118.62 ng m-3 for Tecamachalco, 83.4 ng m-3 for San Agustin and 261.2 ng m-3 for Xalostoc. According to Ontario's air quality standards, the threshold value for mercury vapor in ambient air is 2 mg m-3 on a 30 day average (Mercury situation in Canada, Report # 2, Environment Canada, May 2002). According to these criteria, then, the data reported for Mexico City are within the allowed limits for ambient air, but still 22 times higher than those reported as background concentrations at pristine locations (de la Rosa D.A., Volke-Sepulveda T., Solorzano G., Green C., Tordon R., and Beauchamp S., (2004), Survey of atmospheric total gaseous mercury in Mexico, Atmospheric Environment 38, 4839-4846). These TGM concentrations, measured during the different seasons occurring in the ZMVM, that is, rainy, cold dry and warm dry seasons, will allow us to establish through the integration of time series, block diagrams and the application of basic descriptive statistics, the temporal profile of TGM concentrations at the Iztapalapa, CENICA station during a seasonal year. Likewise, data from the other sites will let us compare the concentration levels among different areas in the ZMVM.
A11A-0006 0800h
Evaluation of Standard Measurement Techniques for Gas Phase Ozone and Nitrogen Dioxide in a Polluted Urban Environment
The performance of standard EPA-certified techniques for monitoring the ambient concentrations of O3 by UV absorption and NO2 by its chemiluminescent reaction with O3 has been evaluated using data from a five-week long field campaign in the Mexico City Metropolitan Area in the spring of 2003. Comparisons of multiple measurements of both O3 and NO2 are described. In particular, open path DOAS measurements of O3 and NO2 and a tunable diode laser absorption measurement of NO2 are compared with co-located standard techniques. The potential interference of gas phase aromatic hydrocarbons to the UV absorption measurement of O3 and the potential interference of gas phase organic nitrates to the standard NO2 measurement are examined. Potential implications for air quality modeling and repercussions for monitoring networks are discussed.
A11A-0007 0800h
VOC Signatures at Selected Urban Sites in Mexico City during the MCMA 2002 and 2003 Field Campaigns
During the MCMA 2002 and 2003 field campaigns, ambient VOC concentrations were measured using automated canister sampling methods at several urban sites within Mexico City. These data, along with previously reported measurements, are examined in terms of the similarities and differences that exist for locations near the urban core, in heavily industrial areas, and at downwind urban receptor sites. Data are also compared to similar measurements for US cities. The use of ratios of compounds at different locations is valuable for highlighting the effects of dilution versus chemical aging during transport from sources to receptors. These ratios can also be used to demonstrate the effects of local industrial sources on the VOC distribution at selected locations.
A11A-0008 0800h
Measurements of Trace Gas Fluxes from the Mexico City Urban Landscape
As part of the MCMA 2003 field campaign, we demonstrated the feasibility of using eddy covariance techniques coupled with fast-response sensors to measure urban CO2 and VOC fluxes from a neighborhood of Mexico City, where the spatial variability of surface cover and roughness is high. Eddy covariance methods were used to measure CO2 and organic olefin fluxes where an open path infrared CO2 sensor was used for CO2 measurements and a Fast Olefin Sensor (FOS) was employed for the olefin fluxes. Concentrations of methanol, acetone, toluene and C2-benzenes were measured with a Proton Transfer Reaction Mass Spectrometer (PTR-MS), and fluxes were obtained using a disjunct eddy covariance technique. Stationarity, spectral and co-spectral analyses of the data demonstrated that the underlying requirements for micrometeorological flux measurements were satisfied. The CO2 flux measurements showed that the urban landscape is a net source for CO2 with the highest emissions during the morning (up to 1.60 mg m-2 s-1), and lower emissions during nighttime. The mean daily flux was 0.41 mg m-2 s-1, which is similar to observations in US or European developed cities. The VOC flux results showed that fluxes exhibit a clear diurnal pattern with a strong relationship to vehicular traffic. These data can be used to help assess the accuracy of gridded emission inventories developed for photochemical air quality modeling in Mexico City.
A11A-0009 0800h
Continuous VOC Monitoring at the CENICA Supersite during April 2000-2004: A Comparison with the MCMA-2003 Campaign
Since 1999, VOC's have been monitored at CENICA, located in the southeast of the Mexico City Metropolitan Area (MCMA), in order to contribute to the understanding of ozone formation and the presence of toxic air pollutants. CENICA was also the supersite of the MCMA-2003 campaign. This work presents an analysis of the total and thirteen specific VOC's (compounds from C2-C9) measured over some days of the month of April from 2000-2004. Hourly measurements were made throughout the year on four minute samples using a humidifier and cryogenic trap. Samples were analyzed with gas chromatography and FID according to the EPA TO-15 method. The highest and second highest total and specific VOC concentrations were observed during the morning (7-9 am) and night period (9-11 pm), respectively. The highest VOC concentrations were observed for propane, n-butane, acetylene and toluene in both periods. Statistical analysis will be presented to determine if there are significant differences between the different years. Correlations among the 13 VOC's indicated common sources for specific compounds. Therefore, the Chemical Mass Balance Model was applied using samples from 8 am of each year respectively. Preliminary results imply that the GLP contribution increased during this five year period and that the vehicle exhaust contribution decreased in the same time.
A11A-0010 0800h
VOC Measurements in Mega-city Tokyo: Behaviors, Sources, and Photochemical Transformations
Volatile organic compounds (VOCs) play important role as precursors for formation of ozone and organic secondary aerosols. In urban regions, VOCs are emitted in large quantities from a wide variety of anthropogenic sources. To characterize behaviors of VOCs in mega-city Tokyo, Japan, we have made measurements of VOCs and oxygenated VOCs using a proton-transfer-reaction mass spectrometry (PTR-MS) technique since April 2003. A positive correlation with CO was generally observed for various VOCs and OVOCs through a year. High concentrations were generally observed under calm wind conditions likely due to accumulation effect. In some cases, enhancements in benzene and toluene concentrations were observed without a corresponding increase in CO. They were observed for particular wind directions. Evaporation of gasoline (refuel loss) and solvent are probably responsible for these enhancements. Diurnal variation with a maximum around noon was observed for acetaldehyde. It was especially evident after removing contributions from primary emissions using CO and it positively correlated with O3.
A11A-0011 0800h
MAX-DOAS measurement of Glyoxal at the MIT in Cambridge during the NEAQS-ITCT 2004 Campaign
During the New England Air Quality Study Intercontinental Transport and Chemical Transformation (NEAQS-ITCT) 2004 Campaign we performed measurements with Multiple Axis Differential Optical Absorption Spectroscopy (MAX-DOAS) at several sites in the northeast of the USA. Thereby scattered sun light was measured at different elevation angles (Multiple Axis) what allows to gain information on the vertical distribution of atmospheric trace gases. At the MIT station in Cambridge, our set-up was optimized to measure glyoxal, which has recently been detected by open-path DOAS in Mexico City and proposed as a new gas phase tracer substance for the chemistry of volatile organic compounds (VOCs). Here we present the first detection of glyoxal by a passive DOAS device. The concentration and vertical distribution of this interesting species are shown and compared with those of NO$_{2}$, and HCHO. Measurements of glyoxal are generally sparse, and as we demonstrate seem feasible with MAX-DOAS on a routine basis, also in semi-polluted urban atmospheres. Such measurements allow access to information on glyoxal precursor VOCs, which due to physical limitations are not directly accessible by passive DOAS devices.
A11A-0012 0800h
MAX-DOAS Network-Measurement of NO$_{2}$, HCHO and SO$_{2}$ during the NEAQS-ITCT 2004 Campaign
From July 1st through August 15th the New England Air Quality Study Intercontinental Transport and Chemical Transformation (NEAQS-ITCT) 2004 Campaign took place. As a part of it we performed measurements with Multiple Axis Differential Optical Absorption Spectroscopy (MAX-DOAS) at six different sites (MIT Cambridge, Thompson Farm (UNH), URI Narragansett, NL Brookhaven, Harvard Forest (Harvard University) and Pinnacle State Park (UAlbany)) and on the research vessel Ron Brown to derive slant column densities of NO$_{2}$, HCHO and SO$_{2}$. Such a comprehensive network of kindred and continuous measurements was assembled for the first time. Thereby scattered sun light was measured at several elevation angles (Multiple Axis). This setup allows to gain information on the vertical distribution of atmospheric trace gases. We present the first results of these MAX-DOAS measurements and show an overview of the regional and temporal variations of the trace gases over the north-eastern States, which have often been called the tailpipe of the USA.
A11A-0013 0800h
A Simple But Comprehensive Methodology To Determine Gas-Phase Emissions Of Motor Vehicles With Extractive FTIR Spectrometry
In this contribution, a methodology to acquire valuable information on the chemical composition and evolution of vehicular emissions is presented. With this innovative experimental set-up, it is possible to obtain real-time emissions of the combustion products without the need of dilution or sample collection. Key pollutants such as CO, CO2, H2CO, CH4, NO, N2O, NH3, SO2, CH3OH, acetylene, ethylene, ethane and total hydrocarbons, most of which are not regulated nor measured by current emissions control programs, can be accurately monitored with a single instrument. An FTIR spectrometer is used for the analysis of a constant flow of sample gas from the tail-pipe into a stainless-steel cylindrical cell of constant volume.(1) The cell is heated to 185 °C to avoid condensation, the pressure is kept constant and a multi-pass optical arrangement(2)is used to transmit the modulated infrared beam several times to improve the sensitivity. The total flow from the exhaust used for calculating the emission can be continuously determined from the differential pressure measurements from a "Pitot" tube calibrated against a hot-wire devise. This simple methodology is proposed for performing state-of-the-art evaluations on the emission behavior of new technologies, reformulated fuels and emission control devices. The results presented here were performed on a dynamometer running FTP-75 and driving cycles typical for Mexico City.(3,4) References 1. Grutter M. "Multi-Gas Analysis using FTIR Spectroscopy over Mexico City." Atmosfera 16, 1-16 (2003). 2. White J.U. "Long optical paths of large aperture. J. Opt. Soc. Am., 32, 285-288 (1942). 3. Santiago Cruz L. and P.I. Rincon. "Instrumentation of the Emission Control Laboratory at the Engineering School of the National Autonomous University of Mexico." Instrumentation and Development 4, 19-24, (2000). 4. Gonzalez Oropeza R. and A. Galvan Zacarias. "Desarrollo de ciclos de manejo caracteristicos de la Ciudad de Mexico." Memorias del IX Congreso Anual, Soc. Mex. de Ing. Mec. 535-544 (2003).
A11A-0014 0800h
Comparison of PAN and Black Carbon Levels in Mexico City: 1997 and 2003
Peroxyacetyl nitrate (PAN) is a secondary oxidant formed by the oxidation of hydrocarbons in the presence of nitrogen dioxide. PAN is a good indicator compound for hydrocarbon reactivity that leads to ozone formation. Black carbon (BC) is formed by incomplete combustion processes such as diesel soot formation and is a good indicator of primary carbonaceous aerosols in urban areas. We used a fast-response luminol method to measure PAN and BC during the Mexico City Metropolitan Area 2003/Mexico City Megacity 2003 field study in April 2003. We compare these results with our previous PAN measurements in Mexico City during February 1997, made with a gas chromatograph-electron capture detector system. The decreased PAN levels observed in 2003 are consistent with the application of emissions controls on spark ignition gasoline-fueled vehicles, leading to lower levels of the nitrogen oxides and reactive volatile hydrocarbons needed to form PAN. Black carbon data for Mexico City in 2003, taken with a seven-channel aethalometer, are compared with data from 1997, estimated from thermal analyses as elemental carbon (EC). The comparison indicates little change in the levels of BC/EC over the six-year period. This observation is consistent with the application of minimal controls to diesel engines, the likely major source of BC in the Mexico City megacity complex during this period. The authors wish to thank the researchers at Centro Nacional de Investigacion en Calidad Ambiental (CENICA), Mexico City. This work was supported by the U.S. Department of Energy, Atmospheric Science Program. We also wish to acknowledge Drs. Mario and Luisa Molina for their help in organizing and directing the Mexico City Metropolitan Area 2003 field study, during which these data were collected.
A11A-0015 0800h
Mobile Laboratory Measurements of Black Carbon and Polycyclic Aromatic Hydrocarbon Emissions in Mexico City: A New Method for Motor Vehicle Emission Inventory Calculations
Aerosol black carbon (BC) and polycyclic aromatic hydrocarbons (PAHs) are two products of carbonaceous fuel combustion that are of major concern for urban air quality and global climate change. As part of the Mexico City Metropolitan Area field campaign in April 2003 (MCMA-2003), a mobile laboratory drove throughout the city and chased vehicles to measure pollutants in their exhaust emissions. The laboratory is a van designed and built by Aerodyne Research, Inc. and is equipped with a suite of gas and particle analyzers, including an aethalometer that measures BC and a photoemission aerosol sensor that measures particle-bound PAHs. The main goal of this research is to determine fuel-based emission factors, or the mass of BC and PAH emitted per volume of fuel burned, for Mexico City's vehicle fleet. We can then calculate the megacity's emission inventory of these compounds, which is important on both the urban and global scales. In previous analyses, the mobile laboratory has been used to target emissions from specific vehicles. While chasing events can be analyzed to obtain emission factors for specific vehicles, data from the entire time period while the lab is driving through the streets, whether chasing individual vehicles or not, can also provide valuable information about mobile source emissions. The laboratory continuously samples ambient air from an inlet at the front of the van, and it is always seeing exhaust plumes from the vehicles around it. This macroscopic approach that considers all vehicles on the road, similar to tunnel and remote sensing studies, complements the microscopic approach that focuses on individual vehicles. We have developed a method that automatically identifies exhaust plumes and quantifies emission factors from data collected by the mobile lab. While 200 individual chasing events were identified during the field campaign, over 40,000 exhaust plume points were identified using the macroscopic approach. The large sample size enables us to estimate fleet-average emission factors and thus the emission inventory. This method is applicable not only to BC and PAH concentrations, but also to other pollutants measured by the mobile lab. For comparison, we also estimate total emissions using an alternative method: multiplying ambient concentration ratios of BC to carbon monoxide by official estimates of carbon monoxide emissions. Results of the two methods agree reasonably well, adding confidence to our estimates.
A11A-0016 0800h
Composition and Sourcing of Aerosol in the Mexico City Metropolitan Area with PIXE/PESA/STIM and Multivariate Analysis
Particulate matter $<$2.5 m in diameter (PM2.5) is a serious concern in megacity air pollution for its possible effects
on human health and climate, and potential role in heterogeneous chemical processes. Determining the chemical composition of
PM2.5 is essential in assessing their effects, and the various aerosol emission sources must be identified in order to
develop effective pollution control strategies.
Samples of PM2.5 were collected in a southeastern site in the Mexico City Metropolitan Area (MCMA) during the MCMA-2003
campaign between April 3 - May 4, 2003 with a 3-stage IMPROVED Cascade DRUM Impactor in size ranges 0.07 - 0.34 $\mu$m (Stage
C), 0.34 - 1.15 $\mu$m (Stage B), and 1.15 - 2.5 $\mu$m (Stage A). Analyses by Proton-Induced X-ray Emission (PIXE),
Proton-Elastic Scattering Analysis (PESA) and Scanning Transmission Ion Microscopy (STIM) were performed to provide 6-hr
averaged concentrations of elements $>$ Na, H, and total aerosol mass, respectively, for each size range. Multivariate
analysis including Positive Matrix Factorization (PMF) was applied to group elements by common factors to identify possible
aerosol emission sources within each size range. Sudden increases in elements characteristic of industrial emissions and
fuel oil suggest manufacturing sources to the north of the city whereas soil aerosols originate from more rural areas to the
south. Sulfur contributes to a significant fraction of PM2.5, in agreement with complementary aerosol measurements taken
during the campaign. Additional trends and diurnal profiles observed for Mexico City aerosol are presented.
A11A-0017 0800h
Chemical Aerosol Characterization Sampling in Santa Ana during the MCMA-2003 Field Campaign
Aerosol samples were collected during the intensive MCMA-2003 campaign in Santa Ana (19.1772$\deg$N, 98.99$\deg$W), Mexico City. This small rural town lies near the southeastern border of Mexico City and on the western rim of a mountain pass that channels the southern outflow of air from the city. Particles smaller than 10 $\mu$m in aerodynamic diameter were collected on aluminum foils using three 8-stage micro orifice uniform deposit impactor (MOUDI), while fine particles (PM2.5) were collected in quartz fiber filters using manual samplers (MiniVol air samplers, Airmetrics). Samples were taken every 3 days starting at 2am in 6 hr intervals (total time 18 hrs for MOUDI and 24 hrs for MiniVol) from April 10-22, 2003. The MOUDI was operated at a flow rate of 30 l/min with calibrated impaction cut-points in the range of 10 - 0.18 $\mu$m; while the MiniVol operation flow rate was 5 l/min. Prior to sampling, the aluminum foils were pre-conditioned (at 450$\deg$C) in a furnace for 8 hrs to eliminate impurities. Both types of filters were weighted using an Ultra Microbalance (Cahn, with a sensitivity of 0.1 $\mu$g) for particulate matter under controlled conditions (20$\deg$C and 50% relative humidity). The aluminum foils were cut in halves, one half for Total Carbon (TC) determination with a thermal method, Evolved Gas Analysis (EGA), and the other half for analysis of inorganic ions (Cl-, NO3, SO42-, NA+, NH4+, K+, Ca2+ and Mg+) by liquid chromatography and mass spectrometer analytic method. Organic and elemental carbon was done according to the IMPROVE Thermal Protocol. Aerosol measurements made with MOUDI showed that the particle size distribution was bimodal in the three sampling periods. During daylight periods, 75% of the collected samples consisted of particles with aerodynamic diameter $<$ 1 $\mu$m whereas the major mass concentration was dominated by particles $>$ 1 $\mu$m during night. PM2.5 results reveal that the highest and lowest levels were obtained during the afternoon (60.6 $\mu$g/m3), and at nighttime (13.89 $\mu$g/m3), respectively. These concentrations are lower than those obtained in different parts of Mexico City such as Tlalnepantla, Ecatepec, Nezahualcoyotl and Cuauhtemoc, using similar equipment during the dry warm season of 2002. Overall, 40% of the total concentration was characterized as carbon, and 10% as ions. Organic carbon represented approximately 80% of the total carbon, while SO42- represented 60% of the total ions concentration.
A11A-0018 0800h
Size, Time, and Composition-Resolved Aerosol Measurements in Mexico City During the MCMA-2003 Field Campaign: The Organic Component
An Aerodyne Aerosol Mass Spectrometer (AMS) was deployed to the CENICA Supersite during the Mexico City Metropolitan Area (MCMA-2003) field study from March 29 - May 4, 2003. Organic aerosols dominate the NR-PM$_{1}$ aerosol concentrations in Mexico City during MCMA-2003, and are the focus of this presentation (inorganic species: Salcedo et al., this conference). We have applied a procedure based on internal AMS tracers (Zhang et al., this conference) to estimate the concentrations and size distributions of primary and oxygenated organic aerosols (POA and OOA respectively). OOA encompasses secondary organic aerosol (SOA) as well as oxidized POA. This method is based on iterative principal component analysis with a custom method that uses AMS {\it m/z} 57 and {\it m/z}44 as initial time series for POA and OOA respectively. During MCMA-2003 POA shows good correlation with primary combustion emissions (such as CO, BC, and NO$_{x}$), and SOA shows correlation with photochemical products (such as O$_{3}$ and glyoxal). Our results show that organic aerosols during MCMA-2003 were comprised of $\sim$35% POA, and $\sim$65% OOA. Intense SOA formation was observed many of the days, which is consistent with the high levels of aerosol precursors (aromatics), UV radiation, and of radicals (OH, HO$_{2}$) measured by other researchers. OOA in Mexico City is likely dominated by SOA from the oxidation of aromatic species. The aerosol size distribution was often bimodal, with a smaller mode, $\sim$100 nm in {\it d$_{va}$},(i.e., aerodynamic diameter in free molecular regime) characteristic of traffic emissions, and a larger accumulation mode ($\sim$500 nm {\it d$_{va}$}) dominated by photochemical products. The ultrafine ($<$ 100 nm) composition is analyzed with collocated measurements from a nano-SMPS and the AMS. Traffic-related POA dominates the ultrafine mode every morning during rush hour. Ultrafine particles in the afternoon contain both sulfate and organics (both POA and SOA). A nucleation event was observed inside the city when the aerosol surface area was relatively low.
A11A-0019 0800h
Measurement of Mexico City Ultrafine Aerosol Size Distributions: Observations of New Particle Formation and Growth
Continuous measurements of the size distribution of atmospheric aerosol in the 3 to 48 nm diameter range were performed in the Mexico City metropolitan area. These measurements were made during the period 10 to 20 April 2003 at a ground-based, mountain pass site in the southeast corner of the Mexico City Federal District and during the period 2 to 11 May 2003 at the CENICA site located near the city center. The objectives of this work were to determine the frequency of new particle formation and to characterize the atmospheric chemical and meteorological conditions that lead to these events. Several new particle formation events were recorded during the study. Events observed in the mountain pass correlate with northerly winds and elevated levels of sulfur dioxide in the mid-morning while events observed in the city correlate with elevated concentrations of sulfur dioxide and low particulate matter mass concentrations in the afternoon hours.
A11A-0020 0800h
Implementation of a Markov Chain Monte Carlo Method to Inorganic Aerosol Modeling: Mexico City Metropolitan Area Case Study
Significant effort has been devoted to collecting data on urban particulate matter (PM) concentrations, and advances in particle measurement technologies have allowed for an increasingly sophisticated picture to be developed. Relative to this, the dataset for the gas phase precursors to the inorganic PM is sparse, despite the necessity of these observations in determining effective control strategies. A Bayesian method has been implemented to exploit the asymmetry between the rich aerosol dataset and the relatively poor dataset on gas-phase precursors. A Markov Chain Monte Carlo algorithm was combined with the equilibrium inorganic aerosol model ISORROPIA to produce a powerful tool to analyze aerosol data and predict gas phase concentrations where these are unavailable. The method directly incorporates measurement uncertainty, prior knowledge, and provides for a formal framework to combine measurements of different quality. Applying the method to data from Mexico City, evidence for stable and metastable aerosols was found, and model predictions relative to the observations and their uncertainties are critically compared. Gas phase concentrations, where unavailable, were estimated including, for the first time in Mexico City, hydrochloric acid. The policy implications of these findings will be discussed, with a focus on the role of ammonia and chloride species on particle formation.
A11A-0021 0800h
Characterization of Particle and Gas Phase Pollutant Emissions from Heavy- and Light-Duty Vehicles in a California Roadway Tunnel
In summer 2004, particle and gas phase pollutant emissions from heavy-duty diesel and light-duty gasoline vehicles were characterized in the Caldecott tunnel, located east of San Francisco Bay. This measurement campaign was the latest of many in the tunnel. In addition to assessing temporal trends in pollutant emission rates, the study is of interest due to recent changes to gasoline composition in California - methyl tertiary butyl ether (MTBE) has been phased out and replaced in part with ethanol. The current study determined mass emission rates (in g of pollutant emitted per kg of fuel burned) of PM2.5, particulate black and organic carbon (BC and OC), and carbon monoxide (CO). The hygroscopicity and optical properties of PM2.5 emissions were also measured: optical absorption was measured using filter-based photometer methods and optical extinction and scattering were simultaneously measured in-situ with a new cavity ring-down instrument. Initial results of the study indicate substantial decreases in mass emission rates of PM2.5, BC, OC, and CO from both heavy-duty diesel and light duty-gasoline vehicles since 1997, when emission rates were previously measured at the tunnel. The decreases were greater for heavy-duty vehicles than for light-duty vehicles, but emission rates of the particulate species are, nonetheless, 10-20 times greater from heavy-duty vehicles. Hygroscopic growth was not evident when particulate matter was humidified from 40 to 80 percent relative humidity, indicating the hydrophobic nature of freshly emitted gasoline and diesel particles, which contained comparable amounts of OC and BC. Other results will be presented, including those pertaining to the measurement of aerosol optical absorption.
A11A-0022 0800h
The Effect of Central American Smoke Aerosols on the Air Quality and Climate over the Southeastern United States: First Results from RAMS-AROMA
Observation shows that smoke aerosols from biomass burning activities in Central America can be transported to the Southeastern United States (SEUS). In this study, the Regional Atmospheric Modeling System - Assimilation and Radiation Online Modeling of Aerosols (RAMS-AROMA) is used to investigate the effect of transported smoke aerosols on climate and air quality over the SEUS. AROMA is an aerosol transport model with capabilities of online integration of aerosol radiation effects and online assimilation of satellite-derived aerosol and emission products. It is assembled within the RAMS, so two-way interactions between aerosol fields and other meteorology fields are achieved simultaneously during each model time step. RAMS-AROMA is a unique tool that can be used to examine the aerosol radiative impacts on the surface energy budget and atmospheric heating rate and to investigate how atmospheric thermal and dynamical processes respond to such impacts and consequently affect the aerosol distribution (so called feedbacks). First results regarding air quality effects and radiative forcing of transported smoke aerosols will be presented from RAMS-AROMA based on assimilation of smoke emission products from the Fire Locating and Modeling of Burning Emissions (FLAMBE) project and aerosol optical thickness data derived from the MODIS instrument on the Terra and Aqua satellites. Comparisons with PM$_{2.5}$ data collected from the EPA observation network and the aerosol optical thickness data from the DOE Atmosphere Radiation Measurements in the Southern Great Plains (ARM SGP) showed that RAMS-AROMA can predict the timing and spatial distribution of smoke events very well, with an accuracy useful for air quality forecasts. The smoke radiative effects on the surface temperature and atmospheric heating rate as well as their feedbacks will also be discussed.
A11A-0023 0800h
Fine Particulate Pollution and Source Apportionment in the Urban Centers for Africa, Asia and Latin America
Fossil fuel combustion for domestic cooking and heating, power generation, industrial processes, and motor vehicles are the primary sources of air pollution in the developing country cities. Over the past twenty years, major advances have been made in understanding the social and economic consequences of air pollution. In both industrialized and developing countries, it has been shown that air pollution from energy combustion has detrimental impacts on human health and the environment. Lack of information on the sectoral contributions to air pollution - especially fine particulates, is one of the typical constraints for an effective integrated urban air quality management program. Without such information, it is difficult, if not impossible, for decision makers to provide policy advice and make informed investment decisions related to air quality improvements in developing countries. This also raises the need for low-cost ways of determining the principal sources of fine PM for a proper planning and decision making. The project objective is to develop and verify a methodology to assess and monitor the sources of PM, using a combination of ground-based monitoring and source apportionment techniques. This presentation will focus on four general tasks: (1) Review of the science and current activities in the combined use of monitoring data and modeling for better understanding of PM pollution. (2) Review of recent advances in atmospheric source apportionment techniques (e.g., principal component analysis, organic markers, source-receptor modeling techniques). (3) Develop a general methodology to use integrated top-down and bottom-up datasets. (4) Review of a series of current case studies from Africa, Asia and Latin America and the methodologies applied to assess the air pollution and its sources.
A11A-0024 0800h
Fine Particulate Pollution and its Impact on Visibility Impairment in the Seoul Metropolitan Area during 2002-2004 Campaigns
In order to investigate the causes for fine particulate pollution and visibility impairment in the Seoul metropolitan area, extensive aerosol chemical and optical monitoring had been conducted at two urban sites, Junnong, Seoul and Younghyun, Incheon during six seasonal intensive monitoring periods (IMP); 5-26 August and 20-28 October 2002, 10-24 January and 6-14 June 2003, and 6-15 January and 13-22 April 2004. Light extinction and scattering coefficient were measured simultaneously with a transmissometer and a nephelometer, respectively. Average light extinction coefficient and visual range were measured to be 569 338Mm-1 and 6.9 5.4km at Junnong, Seoul and 614 409Mm-1 and 6.4 4.7km at Younghyun, Incheon, respectively. Light extinction budget for six major aerosol components; ammonium sulfate (NHSO), ammonium nitrate (NHNO), elemental carbon (EC) and organic carbon (OC) particles, fine soil (FS), and coarse particles (CM) was estimated based on the measured aerosol chemistry data. When the visibility was degraded from the worst 20% to the best 20% condition, percent increased contribution by each aerosol component was estimated to be 28.9% (NHSO), 16.8% (NHNO), 7.4% (OC), 22.4%(EC), 1.2% (FS), and 23.3% (CM), respectively at Junnong, Seoul. Contributions by ammonium sulfate and ammonium nitrate included the effects of relative humidity increase, which accounted for 47.4% and 59.5% of them, respectively. Impact of air mass characteristics on the visibility condition over the Seoul metropolitan area was also analyzed based on the air mass pathway information obtained using the HYSPLIT model.
A11A-0025 0800h
Heavy Metal Content in Airborne Dust of Childhood Leukemia Cluster Areas: Even Small Towns Have Air Pollutants
Currently in the US, there are at least two ongoing clusters of childhood leukemia, where the incidence rate over the last several years has exceeded the national norm. In Fallon, Nevada, a town of 8,000 people, 16 children have been diagnosed with leukemia since 1995, three of whom have died. In Sierra Vista, Arizona, a town of 38,000 people, 12 children have been diagnosed since 1998, two of whom have died. A possible third cluster of childhood leukemia and other cancers is being monitored in Elk Grove, California, a suburb of Sacramento. For the purpose of characterizing the heavy metal content of airborne dust of these three communities, total suspended particulate samples were collected from each town as well as from nearby towns that could be considered as control comparisons. Sampling was done using portable high-volume blowers and glass- or quartz-fiber filter media. Filters were measured for elemental concentrations using inductively coupled plasma mass spectroscopy. To date, our most notable results are from the Nevada region. Compared to other control towns in the region, Fallon had significantly more tungsten in its airborne dust. Uranium was also higher in dust of Fallon than in other control towns. Uranium is a known health hazard, though it is not necessarily specifically related to childhood leukemia. The role of tungsten in childhood leukemia has not been widely studied. However, other research has identified tungsten exposure as an environmental concern in Fallon. A CDC study of human tissue samples from Fallon has shown high tungsten levels in people of Fallon, and a USGS study of drinking water in Fallon also has shown high tungsten there. Tree-ring research on selected trees has shown high tungsten values in recent rings compared to earlier rings. While these multiple indications of tungsten in the Fallon environment do not directly lead to the conclusion that tungsten causes leukemia, they do combine to suggest that biomedical research on the role of tungsten in childhood leukemia is justified. It is also worth noting in this session on megacities that environmental pollution issues are concerns not just of large cities, but also of small rural towns.
A11A-0026 0800h
EVALUATION OF IMPACTS OF LANDUSE CHANGES ON AIR QUALITY IN HYDERABAD METROPOLIS USING REMOTE SENSING AND GIS - A CASE STUDY FROM INDIAN SUB-CONTINENT
Around the world cities in developing countries are rapidly growing as more and more people become urban dwellers resulting in increased level of air pollution caused by changes in transportation, energy production and industrial activities. Air quality is an issue of critical importance in view of the accumulating evidence showing the adverse effects of pollution on human health, agricultural crops, manmade environments and ecosystems. An integrated study for identification of appropriate sites for representative evaluation of air pollution, novel means of monitoring air quality, identifying the predominant sources of pollution, effective assessment of air quality and evaluation of different management strategies essential for the development of a healthy and livable region is carried out for Hyderabad metropolis in India using Remote sensing and Geographical Information System (GIS) based assessment tools. Correlation studies between the concentration level of pollutants in urban air and urban land use are also dealt with. Municipal Corporation of Hyderabad (MCH) is divided into eleven planning zones out of which the present study area i.e. Zone I & IIA comprises of industrial, highly commercial and densely populated areas, apart from medium and sparse residential areas making it environmentally sensitive. Sampling locations were identified based on the land use/ land cover of the region and air samples were collected from areas having varying land use patterns using a high volume air sampler. The samples were then analyzed for the presence of Sulphur oxides(SO--x), Oxides of Nitrogen(NO--x), Total Suspended Particulate Matter(TSPM) and Respirable Suspended Particulate Matter(RSPM) using standard protocols and maps showing spatial distribution of SOx, NO--x, TSPM & RSPM were prepared using curve fitting technique of Arc/Info & ArcView GIS software. Air Quality Index (AQI), indicating the overall quality of air and extent of pollution is also calculated, based on which the entire study area is classified into severely, highly, moderately and lightly polluted areas. Concentration of SOx and NOx were observed to be within limits, while particulate pollutants exceeded the standards prescribed by Central Pollution Control Board (CPCB). The major cause of pollution in the study area is attributed to the increasing vehicular movements and presence of commercial and public related activities such as shopping malls. It is observed for the category of severe air pollution that 42% of pollution is from dense residential areas, 19% from medium residential and 1% load of pollution from other public related activities. Based on the results obtained suitable remedial measures to combat the increasing urban air pollution are suggested in the study area. Key words: Air pollution, Remote sensing, Geographical Information System, Spatial distribution, Air quality index.
A11A-0027 0800h
UV-B Measurements in Mexico City: Comparison with Modeled UVB and Black Carbon
Ultraviolet-B radiation (UV-B) represents a chemically important region of the sun's spectrum. At the earth's surface, UV-B can initiate a number of important photochemical reactions (e.g., ozone photolysis) that lead to the formation of OH radicals. Where levels of nitrogen oxides are high and reactive hydrocarbons are found, as in Mexico City and other megacities, UV-B can initiate photochemical smog formation. We used a broadband instrument to obtain UV-B measurements in Mexico City during the Mexico City Metropolitan Area 2003/Mexico City Megacity 2003 field study. We then used a simple radiation model for the Mexico City latitude, altitude, and time of year to construct UV-B contours for comparison with our results. Early morning discrepancies involve reductions in UV-B that are consistent with the presence of significant levels of BC in the Mexico City environment. During most afternoons, UV-B reductions were dominated by clouds. The results are discussed in terms of the potential impacts of BC on UV-B and downwind photochemical processes. The authors wish to thank the researchers at Centro Nacional de Investigacion en Calidad Ambiental (CENICA), Mexico City. This work was supported by the U.S. Department of Energy, Atmospheric Science Program (Marley and Gaffney), and the U.S. Environmental Protection Agency (Frederick). We also wish to acknowledge Drs. Mario and Luisa Molina for their help in organizing and directing the Mexico City Metropolitan Area 2003 field study, during which these data were collected.
A11A-0028 0800h
The Structure of the Planetary Boundary Layer in the Mexico City Metropolitan Area during the MCMA-2003 Field Campaign
The structure and evolution of the planetary boundary layer over Mexico City was observed by Lidar during a collaborative field campaign in April 2003. A typically complicated layering of different abundant aerosols up to 4500 m above ground made it necessary to develop a new data retrieval technique for the mixed layer recognition, taking advantage of the measured laser light depolarization. Lidar results are discussed and compared with mixing and boundary layer heights retrieved from carbon monoxide and meteorological radiosonde measurements as well as model calculations. The knowledge of the mixing and the stable nocturnal boundary layer height is crucial for the interpretation of the numerous ground-based measurements of chemical gas phase and aerosol components. Integral column measurements like photometer soundings are much more useful in conjunction with altitude resolved profiles, because most of the atmospheric aerosol is concentrated in the boundary layer. Results from different measurement techniques will be combined to present a coherent picture of the boundary layer structure during the campaign.
A11A-0029 0800h
Photochemical and Meteorological Conditions during the MCMA-2003 Field Measurement Campaign
MCMA-2003 was a major field campaign of the atmospheric chemistry taking place in the Mexico City Metropolitan Area (MCMA) in April of 2003. April is in the transition from the dry to the wet season with predominant westerly synoptic winds and intense radiation heating leading to strong thermal mountain flows. Three basic types of meteorological conditions were identified: "Cold Surge", "O3-North" and "O3-South", corresponding to cloudy days associated with "Norte" events, peak ozone in the north of the city, and peak ozone in the south. The circulation associated with these is described both at the regional and local level, as high concentrations of both ozone and primary pollutants for each category make them equally relevant to chemical analyses of the basin. Modified wind roses (time roses) based on time of day categories instead of wind speed categories are used to identify shifts in wind directions associated with slope flows inside the basin and sea breeze flows outside of it. The photochemical episodes are compared with historical data from the RAMA monitoring network to assess the representativeness of MCMA-2003. The analysis of the episodes during the campaign shows the existence of one-day episodes where no build-up of pollutants is needed in order to attain very highly localized concentrations but where multi-day events lead to peaks covering a much larger geographic area.
A11A-0030 0800h
Air Quality and Meteorological Boundary Conditions during the MCMA-2003 Field Campaign
A comprehensive field campaign to characterize photochemical smog in the Mexico City Metropolitan Area (MCMA) was conducted during April 2003. An important number of equipment was deployed all around the urban core and its surroundings to measure gas and particles composition from the various sources and receptor sites. In addition to air quality measurements, meteorology variables were also taken by regular weather meteorological stations, tethered balloons, radiosondes, sodars and lidars. One important issue with regard to the field campaign was the characterization of the boundary conditions in order to feed meteorological and air quality models. Four boundary sites were selected to measure continuously criteria pollutants, VOC and meteorological variables at surface level. Vertical meteorological profiles were measured at three other sites : radiosondes in Tacubaya site were launched every six hours daily; tethered balloons were launched at CENICA and FES-Cuautitlan sites according to the weather conditions, and one sodar was deployed at UNAM site in the south of the city. Additionally to these measurements, two fixed meteorological monitoring networks deployed along the city were available to complement these measurements. In general, we observed that transport of pollutants from the city to the boundary sites changes every day, according to the coupling between synoptic and local winds. This effect were less important at elevated sites such as Cerro de la Catedral and ININ, where synoptic wind were more dominant during the field campaign. Also, local sources nearby boundary sites hide the influence of pollution coming from the city some days, particularly at the La Reforma site.
A11A-0031 0800h
Impacts of Aerosols on UV Radiation and Ozone Formation and Analysis of Chemical Processes using a 3-D Chemical Transport Model in the Mexico City Metropolitan Area
The influence of aerosols on UV radiation is investigated by calculating the photolysis rate coefficients using the NCAR tropospheric ultraviolet and visible radiation model (TUV) constrained by aerosol extinction vertical profiles as well as other optical properties provided by Lidar and spectroradiometer observations. The calculated photolysis rates are validated by measured values for key species. The computed photolysis rates are incorporated into a 3-D chemical transport model CAMx (Environ) to assess the impacts of aerosols on O3 formation in the Mexico City Metropolitan Area. Understanding the chemical processes governing O3 formation and the sensitivity of O3 to emissions reductions is a key issue in formulating an effective O3 control strategy . We performed episodic simulations using the CAMx model and analyzed the chemical processes in terms of the budgets of free radicals, NOy and O3, and O3 production rate and efficiency, which gave us useful information about important chemical processes controlling O3 production and sensitivity to precursor reductions. We analyzed as well the effects of chemistry, transport and deposition on O3 production in Mexico City.
A11A-0032 0800h
Preliminary Analysis of Ozonesonde Data from Houston, TX as Part of INTEX-A, July - August 2004
The Houston area is well-known for its frequent levels of high ozone pollution. The extent of the pollution in Houston has important direct and indirect consequences for the local population, ranging from the cancelling of recess to increased rates of asthma to threats of fines and loss of transportation dollars for failure to comply with EPA standards. Despite these consequences, the Houston area has no established program to monitor ozone concentrations at any altitude in the atmosphere but the surface. During the period July 8 - August 12, we launched 25 ozonesondes that yielded data on the vertical distribution of ozone over the city of Houston as part of INTEX-A and a study sponsored by the Shell Center for Sustainable Development at Rice University. Combining ozonesonde data from Houston with a trajectory model from NASA Goddard provides a powerful approach to interpreting the data, including insight into local and remote contributions to Houston's ozone pollution. Analysis of our data show (1) the impact of remote wild fires on ozone levels above Houston, (2) the amount of ozone that develops over Houston in the course of one day, and (3) the extent of vertical mixing of Houston's ozone pollution, a factor in transport to areas downwind of the city.
http://www.ruf.rice.edu/~ozone
A11A-0033 0800h
Model Analysis of the Impact of Changes in Anthropogenic Emissions on the Air Quality in the Eastern United States
The CALGRID photochemical model is employed to conduct simulations of air quality over the Eastern United States. It has been modified to model particulate matter using both a highly parameterized scheme and the more sophisticated ISORROPIA scheme. Annual emission simulations were made for 1996 and future years 2010 and 2020 using EPA model-ready inputs of meteorology, boundary conditions, and emissions prepared for the first round of the EPA Clear Skies Act modeling demonstration. Several specific analysis periods (days) and annual statistics are analyzed to characterize the differences in the model response between the simple and more complicated particulate modeling algorithms. The results from several sensitivity analyses are presented in order to provide an explanation of the model responses. Limited observational data from CASTNET is used to provide some indication as to how well the two modeling approaches perform. The results from this study will be used by the states in the Ozone Transport Commission (OTC) in their State Implementation Plans.
A11A-0034 0800h
Satellite-based Assessment of Air Quality in Megacities
Aerosol products routinely derived from NASA EOS satellites provide an unprecedented opportunity to monitor air pollution around the globe. In this study, aerosol optical thickness and size information retrieved from MODIS instruments on Terra and Aqua satellites are used to examine the air quality over the world's megacities. Aerosol optical thickness is a column-integrated quantity. It reflects not only the aerosol information at the surface but also the total burden of aerosol mass in the atmosphere. Together with retrieved size information, MODIS aerosol optical thickness products have tremendous potential for the assessment of particulate matter emissions from megacities. Comparisons with ground-based PM$_{2.5}$ data collected in several megacities and ambient extinction coefficient data measured from the United States Interagency Monitoring of Protected Visual Environments (IMPROVE) network will be presented. Seasonal and annual variations of air pollution over numerous megacities and their relation to population and energy utility efficiency will also be discussed.