A14A-01 16:00h
Fast time resolution airborne measurements of PANs during the New England Air Quality Study 2004 intensive
Measurements of PAN and a series of its homologues were made on board the NOAA P-3 aircraft during the New England Air Quality Study (NEAQS) as part of the 2004 ICARTT field intensive. 6 different PAN compounds were measured simultaneously with a time resolution of 2 seconds by employing a Chemical Ionization Mass Spectrometer which was flown on board an aircraft for the first time. Previous methods to measure single PAN species typically had time resolutions between 2 and 5 minutes per sample. Results will be presented from semi-Langrangian studies of the New York City and Boston plumes as they move over New England and the Atlantic Ocean as well as from a nighttime study of these urban plumes. We will demonstrate the capabilities of the new instrument using these results. Emphasis will be placed on the distribution and relative amounts of different PAN species formed in air masses influenced by different sources of VOC as well as on the contribution of PANs to the total amount of reactive nitrogen during the day and at night. The New York City and Boston plumes at times showed considerable influence of biogenic VOCs as indicated by high PAN/ PPN ratios in these air masses. Lower PAN/PPN ratios were observed in pollution encountered over the Gulf of Maine, consistent with simultaneous measurements carried out on board the NOAA RV Ronald H. Brown. Our measurements also imply the existence of several other PAN species which previously have not been measured or extensively studied in the atmosphere.
A14A-02 16:15h
Nitro-PAHs in Mexico City: Can Their Presence Be Attributed to Hydroxyl Radical Reactions?
Nitrated polycyclic aromatic hydrocarbons (nitro-PAHs) are genotoxic species present in ambient air from direct emission sources and as the result of atmospheric reactions of the parent PAHs. Data on selected 2 to 4-ring PAHs and their nitrated derivatives will be reported for samples collected April 27-30, 2003 in Mexico City. 2- Nitrofluoranthene and 2-nitropyrene, isomers formed from atmospheric reactions, were present in higher levels in the filter samples than 1-nitropyrene, an isomer found in direct emissions such as diesel exhaust. Data indicating that these nitro-PAHs were formed from hydroxyl radical-initiated reactions will be presented.
A14A-03 16:30h
On-Road Measurement of Vehichle VOC Emission Measurements During the 2003 Mexico City Metropolitan Area Field Campaign
In the spring of 2003 (April 1-May 5), a multinational team of experts conducted an intensive, five-week field campaign in the Mexico City Metropolitan Area (MCMA). The overall goal of this effort was to contribute to the understanding of the air quality problem in megacities. As part of the campaign the Aerodyne Mobile Laboratory was equipped with state-of-the-art analytical instruments and deployed for measuring a variety of vehicle emissions in real time including CO2, NO2, NH3, HCHO, VOC's and volatile (at 600 °C) aerosol. The on-road measurement of vehicle VOC emissions were performed using a commercial version of the IONICON PTR-MS modified to operate onboard the mobile lab platform. A summary of the PTR-MS results from these and supporting laboratory experiments will be presented and discussed. In particular, selected chase events will be presented to illustrate the utility of the PTR-MS technique for characterizing vehicle VOC emission profiles in real time. VOC emission profiles for different vehicle engine types which include gasoline, diesel and compressed natural gas will be discussed and compared to the measurements from other high time response instruments deployed on the Aerodyne mobile van.
A14A-04 16:45h
Ambient Concentrations and Mobile Sources of Ammonia in Mexico City
Emission of ammonia (NH$_{3}$) to the atmosphere is a major environmental concern and a potential health hazard. As the dominant gaseous alkaline species in the atmosphere, ammonia plays an important role in the dynamics of the atmospheric environment and on air quality. Ammonia is a major source of secondary PM-2.5 particulates including ammonium nitrate and ammonium sulfates. These important constituents of airborne PM-2.5 can contribute significantly to regional haze and visibility problems. They are also regulated under the U.S. "National Ambient Air Quality Standard for Particulate Matter" as a human health hazard. Models of the formation of these particulates are being developed but they depend on both detailed inventories of NH$_{3}$ emissions and on comparison of model results with ambient ammonia measurements. A real time tunable infrared laser differential absorption spectroscopy (TILDAS) instrument was deployed on the Aerodyne Research, Inc. Mobile Laboratory in the Mexico City Metropolitan Area (MCMA) in spring 2003. The Quantum Cascade laser (QCL) based instrument collected ammonia concentration data to characterize fleet average and individual vehicle emissions. Ambient concentration data at several stationary sites were also studied. Gas phase ammonia data will be used to elucidate the formation of ammonium particles in Mexico City. Implications of the results on air quality modeling will be discussed.
A14A-05 17:00h
Nitrogen Oxides (NOy) in the Mexico City Metropolitan Area
Measurements of total nitrogen oxides (NOy) and numerous individual NOy species were carried out over a five-week period in the spring of 2003 as part of a large field campaign in the Mexico City Metropolitan Area (MCMA). The overall budget of the individual NOy components and their evolution during typical diurnal cycles are described. The role of HNO3 and its interaction with the aerosol phase are highlighted. NOy observations are used to evaluate a chemical transport model (CAMx). Comparisons with NOy levels and speciation from previous field campaigns are discussed as insights into the evolving air quality conditions within the MCMA.
A14A-06 17:12h
Characterization and Distribution of Hydrocarbons in Chinese Urban Air
Air samples were collected in 53 different Chinese cities and analyzed for non methane hydrocarbons (NMHC), halocarbons and alkyl nitrates. In order to identify the main sources of the hydrocarbons, cross correlations with ethyne (C2H2) were investigated together with the difference in hydrocarbon composition in different regions of China. Most of the identified NMHCs show a good correlation with C2H2 (R2 $>$ 0.6) suggesting that their primary source is combustion. Some alkanes (mainly short chain linear alkanes), isoprene and toluene showed a lack of correlation with C2H2 suggesting additional sources of these gases. Several source samples were collected to better characterize the composition of fuel such as liquefied petroleum gas (LPG), natural gas and gasoline specifically used in China. The different distribution in mixing ratio throughout the country was also investigated. The lowest mixing ratios were always observed in the less developed and industrialized western provinces of Qinghai (Golmud city) and XinJiang (Urumqi and HaMi), while the highest mixing ratios were measured in the north eastern region, (Beijing and Taiyuan), in the central region (Chongqing and Lanzhou) and in the south eastern region (Suizhou, Changsha and Nanchang). Toluene was also significantly enhanced in the Pearl River Delta region (PRD) in the Guangdong province.
A14A-07 17:24h
Remote Sensing of Glyoxal as a New Atmospheric Tracer for VOC Chemistry and Secondary Organic Aerosol Formation in the Mexico City Metropolitan Area
Air pollution in the Mexico City Metropolitan Area (MCMA) is intimately linked with the photochemical transformation of primary pollutants like VOC (volatile organic compounds) and NOx, which gives rise to the formation of secondary pollutants such as ozone and secondary organic aerosol (SOA) and their associated adverse effects on human health. As part of the field campaign held in the MCMA in April/May 2003, state-of-the-art measurement techniques including open-path Differential Optical Absorption Spectroscopy (DOAS), spectroradiometry, Aerosol Mass Spectrometry (AMS) and Laser Induced Fluorescence (LIF) were located at the National Center for Environmental Research and Training (CENICA) in Mexico City to characterize the gas-phase and aerosol-phase composition of relevance to the formation of ozone and SOA. A first-ever spectroscopic detection of glyoxal (DOAS) in the atmosphere is described. Glyoxal is shown to be a very useful new photochemical tracer for the chemistry of VOC. The time-resolved glyoxal measurements reveal a very efficient VOC oxidation process during morning hours, which is found to be relevant for overall smog formation later in the day. In combination with measurements of the radical precursor substances HONO, HCHO, ozone (DOAS), their respective J-values (spectroradiometry), OH- and HO2-radical concentrations (LIF), speciated aromatic hydrocarbons (DOAS) and chemical composition of the aerosol phase (AMS), the glyoxal data enables assessment of the role of VOC oxidation in the formation of secondary pollutants in the gas- and aerosol-phase by placing a lower limit on the extend of VOC turnover.
A14A-08 17:36h
Separation of Emitted and Photochemical Formaldehyde in the Mexico City Metropolitan Area using a Statistical Analysis and a New Pair of Gas-phase Tracers
In urban air, the presence of formaldehyde (HCHO) is the result of direct emissions from mobile sources (primary HCHO) and of its production by photochemical oxidation of volatile organic compounds (VOC) in the atmosphere (secondary HCHO). HCHO is a known carcinogen, and is further capable to jump-start photochemical smog formation. Pollution control strategies require deconvolution of the amounts of HCHO formed from primary and secondary sources. To separate primary, secondary and background HCHO, a statistical regression analysis of the time series of HCHO from pairs of gas-phase tracer molecules was undertaken. Carbon monoxide (CO) was used as tracer for primary sources; Two different species were compared as tracers for secondary HCHO: glyoxal (CHOCHO) and ozone (O3). These time series were measured at the field campaign supersite located at the National Center for Environmental Research and Training (CENICA) in the Mexico City Metropolitan Area during the MCMA-2003 campaign. In addition, background HCHO measurements were performed outside the city. Correlation coefficients were highest for the CHOCHO-CO tracer pair, indicating that CHOCHO is a better tracer for secondary sources than O3, used previously for this purpose. Results of the analysis are presented for the pre-Easter, Easter week and post-Easter periods. Further, the effect of temperature on the primary and secondary HCHO sources is assessed. On a 24-hour average basis, secondary sources dominate over primary sources. However, during sunrise, when HCHO acts as a radical source to jump-start photochemistry, a significant amount of the HCHO is associated with primary emissions.
A14A-09 17:48h
Mobile IR- and UV-Spectroscopic Measurements of CO, SO$_{2}$ and VOC in Megacities
Three different types of optical instruments have been deployed at a field campaign in the Mexico City Metropolitan Area (MCMA) 2003 within three main applications: 1) Retrieval of total columns of CO at various positions within the MCMA. 2) Emission inventory of VOC (volatile organic compounds) and SO$_{2}$ from a major industrial source in Tula 100km north of the MCMA. 3) SO$_{2}$ emission inventory of the volcano Popocatepetl located nearby the MCMA. The instruments used were: a) A mobile solar FTIR (Fourier Transform InfraRed) system consisting of a fast sun tracker connected to a 0.5 cm$^{-1}$ resolution FTIR spectrometer, measuring spectra between 2 and 14 $\mu$m wavelength. b) A mobile blue sky UV (ultra violet) spectrometer measuring in the 245 to 380 nm region. c) Two open path FTIR spectrometers with 1 cm$^{-1}$ respectively 0.1 cm$^{-1}$ resolution, operating between 2-5.5 $\mu$m and 2-14 $\mu$m wavelength, respectively. The two instruments were located about 5km apart within the MCMA and measured path averaged concentrations of for instance CO, CO$_{2}$, NO, H$_{2}$CO, VOC, CH$_{4}$, N$_{2}$O over 860m and 500m path respectively. In the first application, the mobile solar FTIR measured atmospheric columns of CO at various locations within and outside the MCMA region, in order to investigate both their temporal and spatial variability. This was combined with the two fixed position long path FTIR spectrometers for studying issues like concentration heterogeneity, mixing height, horizontal advection and possibly total area CO emission. A mesoscale meteorological model (MM5) in combination with a chemical model was run by MIT (Massachusetts Institute of Technology) to generate total CO columns for comparisons. The feasibility of the method will be discussed. In the second application, emissions from a major industrial complex consisting of a powerplant, a refinery and a petrochemical industry were studied in Tula (100km north of MCMA). The solar FTIR system was used to retrieve total columns of VOC, and the mobile UV system measured total columns of SO$_{2}$. By traversing the emission plume of the industry, all the absorbing molecules in the plume cross section were integrated. Finally taking the wind speed into account the emission could be derived. Combining these emission measurements with the MM5 model and concentration measurements within the MCMA, the possible impact of this large emission source on the MCMA air quality can be studied. As a third application the mobile UV system was deployed traversing the SO$_{2}$ plume of the volcano Popocatepetl, located in close vicinity to the MCMA. At the same occasion the solar FTIR system measured HCl, SO$_{2}$ and possibly HF columns in the plume. The aim was to derive the emission of these substances from the volcano and to combine it with the MM5 model to see what the possible impact on the MCMA could be.