A21A-0096
Air Quality Measurements From Satellites During the 2008 Beijing Olympics
In preparation for the Olympic games in August 2008, Beijing, China imposed strict controls in industrial
emissions and motor vehicle traffic around the region before and during the event to improve the air quality
for the competitors. We focus on several key industrial and urban pollutants: ozone (O3), nitrogen dioxide
(NO2), carbon monoxide (CO), and sulfur dioxide (SO2) to analyze changes in pollution concentrations over
Beijing, as well as other industrialized regions around the world for comparison. We use remote sensing data
from NASA's Aura Ozone Monitoring Instrument (OMI) and Terra/Measurements Of Pollution In The
Troposphere (MOPITT). Preliminary analysis show a reduction in NO2 concentrations compared to previous
years in August. However, changes in the longer lived trace pollutants such as tropospheric ozone, CO and
SO2 are less apparent and highly variable due the influence of the regional meteorology. In particular,
pollution levels in Beijing depend on whether the prevailing winds are blowing in from the sparsely populated
north or from the heavily industrialized provinces to the south, i.e. the nearby Tianjin area and the more
southeastern Shanghai region. Preliminary back-trajectory analysis reveal air parcels coming from the south
correlate well with high pollution days over Beijing.
http://aura.gsfc.nasa.gov/
A21A-0097
Regional Air Quality in the Vicinity of São Paulo Megacity: Pollution and Health Effects
The transport of pollutants among urban area and their interactions concern an issue in air quality modeling. According to the study performed by Sanchez-Ccoyllo et al., 2006, higher ozone concentrations and particulate matter were found in days when the Metropolitan Area of Sao Paulo, MASP is under circulation of winds from the northeast part of the state to the center of the city. In the northeast of state is localized the Paraiba Valley, which is an industrialized region. Therefore, forecast air quality is important to understand physical and chemistry processes that happen in the atmosphere and to help in the formulation of control strategies to reduce the pollution and consequently the health problems associated. The Weather Regional Forecast Chemical model (WRF-chem) treat the chemical (gas and aerosol) and meteorological on-line and has been used to study the regional air quality of Sao Paulo megacity and their implications in human health. The great problem associated to the application of models for South American is the lack of adequate emission inventory. Therefore a great effort has been done to provide information for the air quality model. Different periods with meteorological and chemical conditions were simulated to evaluate the performance of model. Temperature, humidity, CO, NOx, PM10, O3 (surface and vertical) data were used to validate the model at the first phase of work. The comparison of ozone concentrations simulated and observed in surface showed a correlation coefficient from 0.67 to 0.75 for different air quality stations. Also the vertical ozone profile was in agreement with observations. The region of study (-53.2 to -41.0 and -26.3 to -19.7) has about 57 percentage of Brazilian fleet. Therefore, it is crucial to have studies concerning the forecast of air quality and their health effects, which are being developed.
A21A-0098
Mega-city pollution over East Asia: Satellite Perspective
East Asian pollution is now one of the top growing environmental concerns with far-reaching impacts on the global tropospheric air quality and climate change. Satellite observations of tropospheric composition provide a unique opportunity to characterize mega-city pollution. Here we focuse on the air quality over major East Asian mega-cities: Beijing, Shanghai, Hongkong, Seoul and Tokyo in 2006. We analyzed time series of tropospheric O3, CO, and NO2 over those cites from TES, SCIAMACHY, and OMI. Results from GEOS-Chem global 3-D CTM simulations and corresponding meteorological variables including temperature and precipitation are used to understand and interpret the seasonal variations of those pollutants and controlling factors such as transport. Beijing is the most polluted among the five cities where ~200 ppbv of O3 and ~400 ppbv of CO in the lower troposphere were frequent. Those mega-cities' air quality is mostly affected by industrial/urban emissions and domestic biofuel burning from China, while the contribution from natural pollution (biomass burning and terrestrial biosphere) are fairly small. The difference in seasonal trends and photochemical O3 productivity among the cities partly reflects the different photochemical environment in the different latitudes. The strong summer monsoon over Asia causes seasonal mitigation of pollutions over those mega-cities.
A21A-0099
Tropospheric Ozone and Associated Precursors Over Asian Mega-cities From Satellite Data and Regional Model Predictions
We employ the CMAQ and WRF-Chem regional atmospheric chemistry models to study temporal and spatial variations of ozone (O3) and associated precursors over Asian mega-cities. Boundary conditions of chemical species are provided by the CAM-Chem global model, which is run with the same emissions and meteorological reanalysis data as the regional models. Through coupling global and regional models, we examine how the regional processes such as frontal activities, surface-driven convection, and orthographic transport, which might not be resolved in coarse global models, can affect the export of Asian pollutants. The role of vertical transport on the export of mega-cities pollutions is diagnosed by examining the vertical profiles of carbon monoxide (CO) from the CAM-Chem global model, two regional models, and remote sensing satellite retrievals from MOPITT (Measurements Of Pollution In The Troposphere). We implement satellite data from OMI (Ozone Monitoring Instrument) to examine the chemical evolution of tropospheric O3 and associated precursors over Asian mega cities. Regional to urban scale O3 predictions from CMAQ and WRF-Chem are compared and major mechanisms such as chemical schemes, boundary layer mixing, and vertical diffusion contributing to the large difference between two regional models are discussed. The observations of shorter-lived compounds, such as NO2 and HCHO, complement the CO and O3 data by highlighting source regions. We evaluate tropospheric NO2 column densities calculations with the retrievals from GOME-2 (Global Ozone Monitoring Experiment), SCIAMACHY (SCanning Imaging Absorption spectroMeter for Atmospheric CartograpHY), and OMI. We expect results from this work to improve the ability of satellite instruments to inform ground-level air quality over regions like Asia where in situ measurements are very limited.
A21A-0100
Transport of north China air pollution by mid-latitude cyclones: A case study of aircraft measurements in summer 2007
Meteorological processes such as warm conveyor belts (WCBs) and frontal activities, which are related to extratropical cyclones, have been recognized to play important roles in the long-range transport of air pollutants by lifting them from the planetary boundary layer (PBL) into the free troposphere (FT) in mid- latitudes. To understand the transport mechanism and regional impact of air pollution transport in north and east China by mid-latitude cyclones in warm seasons, an aircraft study was carried out in northeast (NE) China in the summer of 2007. During a flight on 27 June, high concentrations of ozone and related trace gases as well as high values of the aerosol scattering coefficient (Bsp) were observed, with maximum concentrations (O3~ 140 ppbv, SO2 ~ 14.6 ppbv, CO ~ 1185 ppbv) recorded at an altitude of 2.6 km in the FT. In this paper we present a detailed analysis of this flight. Mesoscale meteorological simulations with the Weather Research and Forecasting (WRF) model aided the diagnostic analysis of the atmospheric dynamic structure in the low troposphere and helped in the understanding of the transport characteristics of regional and local air pollution. Based on the WRF output, a Lagrangian particle dispersion model, FLEXPART, was used to conduct backward simulations and calculate the source-receptor relationship. The study was undertaken in a region in NE China adjacent to a warm front associated with a weak cyclone in north China. Trajectory analysis and atmospheric structure analysis suggest that the aircraft sampled both the WCB and warm air frontal zone of the cyclone. The backward Lagrangian simulations show that the observed high air pollution in the FT mostly originated from the North China Plain (NCP), especially the northern part containing the megacities Beijing and Tianjin. Their plumes were vented by a stagnant front, probably through, in part, topographic lifting by the mountains in the north, and then were quickly (within 1 to 2 days) transported in the FT to the study region. After the sampling, the observed air masses were further lifted by the WCB into the middle and upper troposphere, and were exported from Asia toward North America and the Arctic, as shown by trajectory analysis and MOPITT satellite observations of CO. This work highlights that frontal activities and WCBs related to mid-latitude cyclones can also play important roles in PBL/FT air pollution exchange and long-range transport from north and NE China in warm seasons.
A21A-0101
Impacts of East Asian summer monsoon on air quality over China
Tropospheric O3 columns retrieved from OMI and MLS measurements, CO columns from MOPITT, and tropospheric O3 and CO concentrations from TES from May to August in 2006 are analyzed using the Regional chEmical and trAnsport Model (REAM) to investigate the impacts of the East Asian summer monsoon on air quality over China. Computed Monsoon Index and the observed migration of the O3 and CO indicate that the summer monsoon significantly affects the air quality over the southeast China up to the east-central China from mid-June to mid-July. The simulated enhancement of O3 over the western China during summer is dominated by the stratosphere downward flux not by O3 transport from East China. The observed summer variations of O3 and CO distribution patterns due to monsoon circulation over East China are simulated in the model. The pre-monsoon high O3 over the southern China is due to tropospheric photochemical production from pollutant emissions and transport from the stratosphere. Photochemical O3 production is substantially reduced after the monsoon onset. The CO enhancement region over the southern China disappears after the onset of the summer monsoon and re-emerges in August after the monsoon wanes.
A21A-0102
Layered structure of Asian dust and pollutants outbreak in spring
Three-dimensional structures of Asian dust and anthropogenic pollutants transport occurring successively during May 2007 were clarified using results of space-borne backscatter lidar (NASA/CALIPSO), NIES ground lidar data and results simulated with a data-assimilated version of a dust transport model (RC4) and US EPA-CMAQ. First large scale outbreak occurred in May 7-9 was characterized by the elevated dust layer height at 2500-4000 m, and anthropogenic pollutants below the dust layer over the Japan, which indicates the dust and pollutants were transported in decoupled condition. Another large outbreak was occurred during May 25 - 28. In this case, we found that the dust and anthropogenic pollutants were mixed within the planetary boundary layer over the Japan. These transport characteristics of dust and pollutants were well simulated by RC4 and CMAQ, both in concentration level and horizontal/vertical scale. Based on CALIPSO and RC4/CMAQ, two significant transport mechanisms of Asian dust/pollutants in the PBL and free atmosphere were clarified: a low level dust outbreak within the dry slot region of a well developed low- pressure system, and formation of an elevated dust layer within the warm sector of a low-pressure system. We will also show clear 3D view of dust/pollutants transport based on CALIPSO and RC4/CMAQ model to help the understanding of large-scale outbreak of dust and pollutants.
A21A-0103
Indication of Long Range Transport by Gaseous Organic Compounds
Continuous hourly observation of ambient non-methane hydrocarbons (NMHCs) was performed by a monitoring station situated in the Taipei metropolitan area. While the original purpose of the NMHC measurements was devoted to the characterization of ozone precursors, other novel applications from the observation has also been developed. In this study, ratios of some long-lived species were used as sensitive indicators of long-range transport (LRT) of continental air masses arriving at the metropolis. Ratios of ethane to propane or butane can serve as these indicators to distinguish the prevailing air masses of LRT or domestic circulation during spring time when frontal events are frequently. Aged continental air masses carried by the winter monsoon are characterized by higher values of ethane/n-butane, in contrast to the baseline values of 0.86, typical of fresh emissions. The abrupt changes from domestic to LRT conditions in this urban basin can be sensitively reflected on the variation of the ethane/n-butane ratios, which is also consistent with the change of ozone concentrations. Continental air masses as indicated by the chemical indicator were featured by higher ozone levels and minimal NOx, which poses a sharp contrast to the periods when the monsoon subsided and the air quality was control by domestic emissions and photochemistry.
A21A-0104
Meteorological Controls on Tropospheric Constituent Variability
We examine the coupling between meteorological variability and chemistry in a series of decadal long hindcast simulations using global models of chemistry and transport. These simulations are driven by NCEP (National Center Environmental Prediction) meteorological reanalysis or by general circulation models forced by observed sea-surface temperatures (i.e., in an AMIP configuration). The simulations show significant interannual variability in tropospheric ozone on the decadal timescale with a significant increase in tropospheric ozone beginning in the early 1990s. Model analysis indicates this increase is due to an increase in stratospheric ozone, an increase attributed to large-scale changes in the atmospheric circulation. The ozone increase is in substantial agreement with a number of long-term measurements of background ozone including measurements from Macehead Ireland, the Western United States, European mountain sites, and MOZAIC. We compare model results to measurements at these sites.
A21A-0105
Investigation of the Los Angeles Basin Atmospheric Sulfur Budget
Airborne sulfur, as gas phase SO2 and particle phase SO42-, was measured in Southern California by in situ instruments aboard the NASA DC-8 during the summer 2007 TC4 and summer 2008 ARCTAS/CARB missions. Two chemical ionization mass spectrometers with differing ionization methods provided independent measurements of SO2. High-resolution time-of-flight aerosol mass spectrometry and a mist chamber / ion chromatography system provided independent measurements of SO42-. Ion chromatography was used to measure SO42- in aqueous extracts of bulk aerosol samples. Observed sulfur concentrations are considerably greater than those predicted from known sulfur sources. We investigate previously underrepresented sulfur sources from ship and aircraft emissions.
A21A-0106
A Seasonal Modeling Study of Air Quality in Central California
Tropospheric ozone has been a continuing research and regulatory concern due to its adverse health effects and its importance in atmospheric chemistry. Photochemical air quality models integrate scientific understanding of how pollutants evolve in the atmosphere at regional or larger scales and have played an important role in developing air quality management plans. Current practice to develop control strategies for ozone precursors is based on simulating short ozone episodes with the 'worst case' weather conditions. There are concerns about the representativeness of such episodes, and about models being tuned to perform well by adjusting input data and model parameters. In our research, we seek a more comprehensive evaluation of air quality model performance, and new insights into questions such as appropriate air pollution control strategies and inter-basin transport of ozone and its precursors, through application of an air quality model to Central California for an entire summer season. Ozone air pollution problems in Central California are severe and not improving. Here we report results from application of the Community Multi-Scale Air Quality model (CMAQ) to the Central California Ozone Study period in 2000 (June to Oct.). Gridded meteorological and emission inputs are developed to reflect variability occurring on diurnal, weekly, and seasonal time scales. Driven by these inputs we assess model skills at predicting 1-h and 8-h average ozone concentrations, as well as ozone precursors, across a range of days and locations, with wide air quality variations seen in both space and time over the entire summer season. We compare modeled and observed ozone responses to changes in meteorological fields (temperature and flow patterns) and emissions. The model shows consistent performance in the San Joaquin Valley in terms of characterizing observed ozone variabilities during different pollution episodes and across the summer season. Ozone sensitivity regimes are reasonably reproduced in the valley. Model performance in the coastal regions is more sensitive to uncertainties in the wind fields under different synoptic conditions.
A21A-0107
Satellite observations of megacity air pollution, biomass burning emissions, and their long- range transport
Recent NASA and Eumetsat satellites offer unparalleled capabilities for remote sensing of air quality throughout the troposphere. Combining both active and passive remote sensing, these instruments probe atmospheric aerosols, clouds and trace gases across the spectrum from the ultraviolet to the microwave. Onboard the Aqua satellite leading NASA's A-Train afternoon satellite constellation, the Atmospheric InfraRed Sounder (AIRS) and Advanced Microwave Sounding Unit (AMSU) see 70% of the Earth both day and night and provide detailed vertical retrievals of temperature and water vapor and weighted free tropospheric concentrations of CO, CH4, CO2, and O3. AIRS's broad horizontal views are complemented by more detailed vertical profiles of CO and O3 afforded by the Tropospheric Emission Sounder (TES) onboard the Aura satellite bringing up the end of the A-Train 8 minutes behind Aqua in the same orbit. During the daytime, the Ozone Monitoring Instrument (OMI) also onboard Aura provides retrievals of total column SO2, NO2, HCHO, CHO-CHO, and O3, and information on the abundance and absorption of aerosols in the free troposphere. Total column aerosol information is retrieved from observations of the MODerate resolution Imaging Spectroradiometer (MODIS) onboard Aqua. Additional information on the vertical distribution and shape of aerosols comes from the CALIOP lidar onboard the Calipso satellite in the middle of the A-Train. Providing coverage from morning orbits are NASA's Terra satellite containing another MODIS and the Measurement Of Pollution In The Troposphere (MOPITT) CO monitoring instrument and Eumetsat's Metop-A satellite carrying the Infrared Atmospheric Sounding Interferometer (IASI) with similar capabilities to AIRS. We will present integrated analyses using these diverse measurements to observe temporal changes in air pollution over several densely populated areas including the Sichuan Basin, China's north coastal plain, and Mexico City. In addition, we will present satellite observations of long-range transport of air pollution and biomass burning emissions.
A21A-0108
Measurements of Ozone, Lightning, and Electric Fields within Thunderstorms over Langmuir Laboratory, New Mexico
A field project was conducted at the Langmuir Laboratory for Atmospheric Research during the summer of 2008 in an effort to better understand the direct production of ozone within electrically active storms. Five balloon flights were successfully launched into thunderstorms during this project. In situ measurements from the balloon instrument package included ozone mixing ratio, electric field strength, meteorological variables, and GPS location and timing. Lightning discharges were identified within each storm using a ground based lightning mapping array. The data show that the instruments ascended through regions of high electric fields within the sampled storms, and in some cases the balloon was in very close proximity to lightning. Relationships between electric field, lightning, and ozone observed during these flights will be discussed.
A21A-0109
Improved Tropospheric Ozone Residual and Comparisons to the GMI Model
Our tropospheric ozone residual (TOR) is produced by subtracting the stratospheric ozone column measured by MLS and the tropospheric ozone column measured by OMI. In our approach we use backward and forward trajectories from four days of MLS V2.2 measurements to boost the horizontal resolution of the stratospheric ozone field. The MLS stratospheric column is then subtracted from the OMI Col. 3 total ozone column. High reflectivity scenes (clouds) are no longer discarded – the OMI cloud pressure and radiative cloud fraction is used to adjust the surface pressure to the cloud centroid pressure. The subsequent TOR fields are validated by comparing them to ozonesondes. Our TOR fields show a 0.8 correlation to sonde columns; a clear improvement over earlier calculations. OMI-MLS TOR from 2005 and 2006 are compared with the Global Modeling Initiative (GMI) derived tropospheric column. The results show that the OMI-MLS TOR underestimates the tropospheric column. GMI tropospheric column and OMI-MLS TOR compare better if the lowest 1.5 km of the GMI column is excluded. This is consistent with a global -7 DU low offset from the sonde columns that is probably due to lack of OMI boundary layer ozone sensitivity. The GMI model zonal distribution also shows relatively higher tropospheric columns at mid latitudes and lower column amounts at high latitudes compared to the OMI-MLS TOR.
A21A-0110
The Impact of ENSO on Surface Ozone Concentrations Over California
Casual examination of the number of days per year in which southern California experiences unhealthy (>84ppb) levels of surface ozone shows that there is significant inter-annual variability in yearly mean surface ozone concentration. Furthermore, the years of known major El Nino/Southern Oscillation events (e.g. 1983 and 1997) seem to have less days with high ozone concentrations. In this study, we examine the processes by which surface ozone over California is impacted by inter-annual climate variability using four dimensional statistical analysis techniques, with specific attention paid to the effect of the El Nino/Southern Oscillation (ENSO). The data sets we examine include the California Air Resources Board's observed surface ozone time series, the National Center for Environmental Prediction's global reanalysis data sets, and the University of Washington's Joint Institute for the Study of the Atmosphere and Ocean's Cold Tongue Index time series, with all data sets spanning the period 1972-2006. We employ several statistical methods in this study, including single and multiple linear regression, empirical orthogonal function analysis, and maximum covariance analysis. Initial results indicate that a southern shift in the mean track of mid-latitude cyclones entering the west coast â€" a phenomenon linked to ENSO events - may be responsible for altering the stagnation time period of air masses over California. We also explore inter-regional differences in surface ozone sensitivity to ENSO and other global climate processes amongst various air basins within California.
A21A-0111
Impact of the Atmospheric Transport on the Seasonal Variations and Trends of the Surface Ozone Concentration at Caucasian and Central European Mountain Sites
An analysis of the atmospheric transport influence on the seasonal variations and trends of the surface ozone for two mountain sites, namely Kislovodsk High Mountain Station (KHMS) in Caucasus, Russia (43.7°N, 42.7°E, 2070 m asl.) and Jungfraujoch (JFJ) in Switzerland (46.5°N, 7.9°E, 3580 m asl) will be presented. Transport patterns are analyzed using 3D LAGRANTO trajectories. Main transport directions are obtained with the help of k-means trajectories clustering for the period 1990-2006. For each selected cluster average seasonal cycle and trends at two mountain locations are analyzed. Due to non-monotonous behavior of the trend the entire period is divided into two subsets (1991-2001 and 1997- 2006) which are studied separately. For both sites (JFJ and KHMS) the highest spring maximum is observed in May in the cluster, originating in East Asia and traveling to both sites with the longest contact with the upper free troposphere. Moreover, for both locations the excess of the summer maximum above the spring one is observed in the cluster of the local/regional transport due to ozone photochemical production in the polluted continental PBL. Trend of the surface ozone concentration at JFJ in 1991-2001 is connected with increased ozone concentrations in the free troposphere of mid latitude over West Atlantic/USA influenced by stratospheric concentration increase (most positive spring trend in trans-Atlantic clusters). The response to the regional European emission decrease observed in the local/regional advection cluster is less important but it is contributing to the seasonality of the trend. In 1997-2006 the trends at JFJ are more connected with European emissions regulations (the strongest trend are in the cluster of local/regional advection). The strong negative trends of the surface ozone concentrations at KHMS during both considered periods (1991-2001 and 1996-2007) are likely to be associated with different regime of emission (both of the local and regional scale), with abrupt emissions reduction in the beginning of 1990s in Former USSR and economical recovery during more recent period. The mentioned trends are best seen in the cluster with local/regional transport. Other reasons are also discussed in the presentation. The work is financially supported by the Swiss National Science Foundation (JRP IB7320-110831), European Commission (Marie-Curie IIF project N 039905 - FP6-2005-Mobility-7) and Russian Foundation for Basic Research (projects 06-05-64427 and 06-05-65308) and contributes to ACCENT T&TP project.
A21A-0112
Trajectory Analysis on Ozone Changes at Jungfraujoch (Switzerland) in 1990- 2005
Ozone measurements at Jungfraujoch (JFJ) covering the period 1990-2005 are investigated in this study. Increasing trends with the maximum +0.63±0.22 ppb/y in winter and the minimum +0.4±0.35 ppb/y in summer are determined. The influences of air masses from various source regions on ozone trends are examined using 10 days backward trajectory analysis. Air masses arriving at JFJ are firstly categoried into European planetary boundary layer (PBL) air and background air. Positive trends on ozone are found for both European PBL air and background air, and to be more evident in winter than in the other seasons. It is also found that the exposure time to the European PBL air gradually increased in winter for the period 1990-2005. A stronger increase of European PBL air advection is found in the most recent years for all seasons, implying that the exposure time of JFJ site to the free troposphere is decreasing. A rough study on the variations of PBL height suggests deepening PBL height might partly be the reason. Furthermore, individual source regions of background air are identified using a series criteria applied to trajectories. Simple linear trend analysis is applied to ozone measurements related to the individual source regions, respectively. Strikingly, ozone from all source regions shows an increasing trend throughout 1990- 2005 with a similar magnititude. Investigation on the occurrence of air mass from the individual source regions shows that European PBL air and free tropospheric air are the two dominating air flow regimes, and the increase on European PBL air is balanced mainly by the free tropospheric air, whose occurrence shows an evident decline from about 60% in the earlier 1990s to about 40% in the recent years. In addition, we examine contributions of the individual source regions to ozone budget at JFJ. The results show that in winter time ozone contribution of the free tropospheric air is decreasing while that of European PBL air is increasing. Whereas in other seasons, large inter-annual variations are obvious. Trends on the contributions depend to a large extent on the selected time periods. In general, the negative anomalies in 1992-1993 due to Pinatubo eruption and positive anomailies in 1998-1999 due to large El Nino event, are less important for ozone trends.
A21A-0113
Seasonal and Interannual Variations of O3 and CO at a rural site near Beijing
The Miyun station, a rural site 100 km northeast of Beijing urban center, is one of the few surface stations in China providing high quality, continuous measurements of O3 and related species (CO, CO2, NO, NOy, and SO2) over a relatively long period (years). Seasonal and interannual variations of O3, CO and their relationships at Miyun during the period 2005-2008 are summarized and analyzed using a 3-D global chemical transport model (GEOS-Chem) and its nested-grid higher-resolution version over China. Monthly mean mixing ratios of O3 peak at 70 ppbv in June at Myun. Simulated O3 budgets suggest that net photochemical production of O3 can reach up to 40 ppb/day at Miyun in summer, roughly balanced by losses of O3 by dry deposition at the surface and export out of the region. Concentrations of O3 were found to be significantly lower in August 2008 as compared to the same month in 2006 and 2007. The changes are attributed to variations in meteorology and to reduction in anthropogenic emissions of O3 precursors associated with the strong emission control measures during the 2008 Summer Olympics Games in Beijing.
A21A-0114
Are Changes in Ground-level Ozone Concentrations in line with emission changes?
Over the last 15-20 years European countries have implemented measures to reduce the emissions of SOx, NOx, NMVOC, NH3 and CO. The rationale is to reduce the sulphur and nitrogen fluxes at ecosystems as well as to reduce the exposure of humans to elevated ozone concentrations. This has resulted in a substantial European wide reduction of these emissions, albeit that timing and size of the emission reduction varies from country to country. Modeling studies have shown that in response to the emission changes the ozone concentrations in the upper part of the distribution (90-percentile and higher) should drop. An analysis of time series of ozone sites indicates that in the first part of the 1990s high ozone concentrations have decreased but that since 1996/7 the levels have stabilized. This lack of a downward trend over the last 10 years is seen at various regions in Europe. Comparison with time series of ozone concentrations from dispersion models might shed light on the causes of the discrepancies between observed and expected ozone trends.
A21A-0115
Estimation of summertime tropospheric ozone distribution over North America: comparison of the Four-Dimensional Variational Data Assimilation to sequential sub-optimal Kalman filtering
4D-variational or adjoint-based data assimilation provides a powerful means for integrating observations with
models to estimate an optimal atmospheric state and to characterize the sensitivity of that state to the
processes controlling it. We estimate the 2006 summer time distribution of North American tropospheric
ozone through assimilation of tropospheric ozone profile retrievals from the Tropospheric Emission
Spectrometer (TES) into the GEOS-Chem global chemical transport model based on a recently-developed
adjoint model of GEOS-Chem. We also compare the estimated ozone distribution produced by the 4-D
variational method to ozone estimated from a sequential sub-optimal Kalman filter approach. We quantify the
differences in the constraints on the spatial distribution of ozone provided by these two different assimilation
approaches with respect to the IONS ozone sonde campaign over North America and the sensitivity of those
differences to ozone precursors.
http://people.cs.vt.edu/kumaresh/GCv7_ADJ_Users_Manual_draft.pdf
A21A-0116
Comparison of Airborne Lidar Measurements of Ozone to Model Analyses During the INTEX-B Field Experiment.
Large-scale distributions of ozone (O3) and aerosols were measured with a differential absorption lidar
(DIAL) on the NASA DC-8 aircraft during the Megacity Initiative: Local Global and Research Observations
(MILAGRO) and Intercontinental Chemical Transport Experiment - Phase B (INTEX-B) field experiments
conducted from 24 February - 22 March 2006 and 17 April - 15 May 2006, respectively. Remote O3
and multi-wavelength aerosol backscatter and aerosol depolarization profiles were simultaneously measured
below and above the DC-8 along its ground track.
During the INTEX-B Pacific phase, long-range transport
of aged and relatively fresh Asian pollution was often observed in the free troposphere in eastern Pacific.
Average latitudinal and longitudinal variations of O3 and aerosols have been derived from the remote
and in situ O3 data for INTEX-B. This paper presents comparisons between the measured averaged
tropospheric O3 cross sections and analyses from several chemical transport models demonstrating
that they have general agreement in atmospheric structure and pollution layer features. However, several
general trends were found between the observations and the models. Compared to DIAL measurements, two
models underestimate O3 by 2-10 ppbv in the lower troposphere (0-6 km) and all the models
overestimate O3 in the upper troposphere (10-12 km) by 8-20 ppbv. The O3 difference between
models and DIAL measurements do not show significant trends over the range of latitudes (22-61 N)
observed. The contribution of stratosphere-troposphere exchange to the latitudinal variation of O3 over
the Pacific has also been examined, and these results will also be presented.
A21A-0117
The response of ozone to transportation technology and policy options
As the global economy grows, there is a corresponding increase in the number of passenger cars on the road and in the volume of goods shipped. Building on novel methods to estimate these transportation emissions, we evaluate the regional air quality impacts of personal vehicles and heavy-duty diesel vehicles (HDDV) for freight transport. In particular, we quantify the potential of technological and policy-based solutions to reduce mean ozone concentrations and the frequency of high ozone events. Although transportation contributes to a range of air quality challenges, ozone chemistry is particularly sensitive to vehicle emissions, with on-road vehicles accounting for 44 percent of all man-made U.S. NOx emissions, and HDDV accounting for nearly 42 percent of this on-road contribution. Our studies focus on the Upper Midwestern United States, where urban development, agricultural activities, lake effect meteorology, and cross-continental freight transport are all major drivers of ozone chemistry and transport. Results will be presented from a range of recently completed and ongoing studies evaluating the ozone impacts of urban vehicle travel, the response of freight emissions to fuel-conserving speed reduction measures, and the consequences of increased biofuel use.
A21A-0118
Changes in Summertime Surface Ozone during the Last Decade over Europe
Long-term trends in summertime surface ozone over Europe are examined using observations from several ground-based European sites (WDCGG and EMEP) and a global chemistry transport model (GEOS-Chem). A simulation that includes interannually varying meteorology and emission inventories from various geopolitical regions as well as several other potentially important factors was conducted from 1991 to 2005. Cumulative probability distributions of hourly daytime surface ozone concentrations in summer are compared between two periods, 1991-1994 vs. 2001-2005 (excluding the anomalously hot year 2003). The observed concentrations have decreased at the high end of the probability distribution and have increased at the low end. The observed crossover is captured by the model at an equivalent ozone concentration (around 40 ppb) but at a lower percentile range (around the 32th percentile) in comparison with the observations (around the 42th percentile). The reasons of this crossover is examined using multiple sensitivity simulations that investigate the influence of emissions and meteorology.
A21A-0119
Meteorological Controls on Spring Ozone Variability in Lower Troposphere in Northeast U.S.: Implications for Stratospheric Intrusions
We use a correlation-based classification algorithm (map typing method) to identify the major synoptic-scale weather patterns modulating the spatial and temporal variation of ozone (O3) in the lower troposphere in the Northeast U.S. during springtime. A 5-year data set comprised of O3 observations from the EPA AIRNOW and the AIRMAP networks that includes an elevated background monitoring site in rural New England (Mount Washington Observatory - MWO, 44.3N, 71.3W, 1910m asl) is used. The meteorological data consists of hemispheric analyses from the NCEP Global Final Analysis, surface weather maps from Unisys Weather (http://weather.unisys.com/), local surface and sounding observations from NOAA/NWS sites, and surface observation from the AIRMAP sites. Using these data sets, we seek to quantify the relative contributions of different synoptic-scale circulation processes to the O3 enhancement in the lower troposphere of Northeast U.S. We estimate that the dynamical effect (resulting from upper air subsidence) is about one third of the photochemical effect, with the former occurring with lower frequency and less O3 enhancement. Case studies of O3 events observed at MWO are also discussed to illustrate how short-term O3 varies with synoptic conditions. Our data analysis forms a basis for evaluating a 3-D chemistry transport model's ability to reproduce synoptic-scale O3 variability and quantify the contributions of different processes influencing O3 on the regional scale.
A21A-0120
The Interannual Variability of Winter Ozone in Northeast U.S.
A multiyear (2001-2007) record of O3 observations is available at the Mount Washington Observatory (MWO, 44.3N, 71.3W, 1910m asl) from the AIRMAP program at the University of New Hampshire. The length of O3 dataset at this elevated background monitoring site allows us to examine the interannual variability of winter O3 in the lower free troposphere in Northeast U.S. This work was motivated by the negative O3 anomaly observed at MWO in winter of 2003, during which period the O3 was about 10 ppb lower than other years. The vertical structure of winter seasonal mean O3 as indicated by MOZAIC data shows similar lower values in 2003 as compared to other years below 4 km, while O3 was relatively higher above 4 km. Aiming to understand the dynamical and photochemical factors controlling the winter O3 anomaly in 2003, we conducted comprehensive meteorological analysis to illustrate how the interannual variability of winter O3 was related to synoptic conditions in Northeast U.S., and examined the photochemical aspects of air masses reaching MWO in terms of O3-CO relationship. We find that the unusual low O3 observed at MWO in winter of 2003 can be explained by a major southward shift in the jet stream resulting in less photochemical activity, and the retreat of the Bermuda High causing less downward transport of O3. In the context of free tropospheric O3 budget analysis with a 3-D CTM, we further quantify relative contributions of dynamic and photochemical effects in winter O3 in the Northeast U.S.
A21A-0121
WRF-Chem Regional Modeling of the Mid-Atlantic: Comparison with Aura and Ground Based Measurements
Trace gas simulations using the Weather Research and Forecasting model with integrated chemistry (WRF- Chem Version 3) for July 2007 are applied to analyze surface and satellite measurements to understand the summertime transitions of key constituents during air pollution episodes in the Mid-Atlantic region. Surface observations from the AIRNOW and remote sensing NO2 and O3 tropospheric measurements from Aura's OMI and TES instruments are analyzed. The relatively high spatial resolution and daily global coverage of the OMI and TES instruments make them well-suited for monitoring tropospheric pollution on regional scales. WRF-Chem allows us to evaluate satellite measured highly variable species such as tropospheric NO2 and O3 on scales on which in situ measurements are insufficient for validation. The ability of OMI and TES instruments to capture high pollution episodes will be investigated.
A21A-0122
A hybrid model combining deterministic, grid-average chemistry transport model concentrations with statistical sub-grid scale variability
Meso-scale chemistry transport models (CTM) have been widely used for urban air quality forecasts but their low horizontal resolution (few kilometers) prevents them to assess pollution exposures within cities. We propose a sub-grid scale model, that takes into account anthropogenic, surface emission heterogeneity and models pollutants variability at scales smaller than model resolution. Grid average emission flux is split into a sub-grid mosaic of emitting surfaces, according to the type of emission source (traffic, residential, use of solvents etc...). Modeled sub-grid concentrations define a statistical variability that is attached to the deterministic CTM concentration providing a description of the unresolved, finer scale. The model is implemented into an existing CTM and results of a 3-months simulation over Paris (June 1st to August 31) are compared to surface measurements at traffic and residential stations. Sub-grid model is able to differentiate correctly pollutants concentrations over the defined micro-environments (close to streets or over residential areas) improving correlation with measurements up to 25% for [PM10] and up to 72% for [NO2]. Sub-grid model concentrations can decrease model bias upto 30% for [NO] and 11% for O3 compared to the grid-average concentration. An additional sensitivity study focuses on the chemical production of a secondary pollutant (ozone) within sub-grid simulations. O3 sub-grid scale variability is found to vary by a factor of 5 depending on the photochemical regime, suggesting that established indicators of the chemical regime can be also useful for the prediction of ozone small scale variabiality.
A21A-0123
Uncertainty in Deriving Atmospheric Perturbations due to Aviation, Shipping, and Road Transport
A preponderance of evidence from atmospheric measurements, laboratory work and chemistry-transport modeling (CTM) demonstrates that emissions from the transport sector are altering the composition of the global atmosphere in ways detrimental to climate and air quality. CTMs are the essential tools for quantifying these changes over seasons and scenarios. We look at some results from the EU QUANTIFY project -- which UCI participated in -- whose objective is to quantify the climate impact of transportation emissions for both present and future. We have results from CTMs using the same emission inventories and meteorological fields. We examine the range of model results for the impact of the transport sector on tropospheric ozone as a possible measure of uncertainty. In addition we perform a series of sensitivity studies with the UCI CTM. We select key uncertainties in our own model (e.g., lightning NOx, scavenging, convection) to understand if these can explain the differences across the QUANTIFY models, and whether the variance across this ensemble of models may represent some of the uncertainty in this assessment.
A21A-0124
Probabilistic Estimates of Surface Ozone Concentration Derived Using an Ensemble of Model Configurations, Direct Sensitivity Calculations, and Bayesian Model Averaging
An ensemble of deterministic simulations is frequently used to create probabilistic estimates that account for uncertainty. A challenge with applying these approaches for simulations of ozone concentration is that chemical transport models require significant input data and computational resources to complete a single simulation. This research offers a computationally efficient approach to create an ensemble of model runs based on a set of inputs that is a more realistic characterization of the uncertainty in the meteorological simulation, boundary conditions, and emissions fields. An ensemble of Community Multiscale Air Quality Model with Decoupled Direct Method (CMAQ-DDM) simulations is used to generate large member ensembles while avoiding the computational cost of running the regional air quality model multiple times. Different approaches for generating the ensemble members are explored by allowing changes in the spatial variation of the boundary conditions and emissions values, rather than by adjusting them by a constant factor over all grid cells and hours. The Bayesian Model Averaging (BMA) statistical technique is used to weight each individual ensemble member based on how closely they match observed values. The final predictions provide a probability distribution of ozone concentration at any given location and time, rather than a single "best" estimate. These methods are applied to 2002 daily ozone data from a set of Air Quality System (AQS) monitoring stations in the South East to select a set of weighted ensemble members that have minimum spread but still capture the variability in the observations. Using additional observations, we evaluate the resulting ensembles and find that they provide a high level of reliability, resolution, and sharpness.
A21A-0125
Trends, seasonal cycles, and interannual variability in the isotopic composition of nitrous oxide between 1940 and 2005
We present measurements and analysis of the isotopic composition (δ15Nbulk, δ15Nα, δ15Nβ, and δ18O) of nitrous oxide in 50 samples of tropospheric air collected at Cape Grim, Tasmania between 1978 and 2005 and in 11 samples of firn air from Law Dome, Antarctica, with mean ages dating from 1940 to the 1990s. Over this 65 year period, the isotopic compositions show overall decreasing trends, consistent with previous firn air measurements and with the prediction that the increase in atmospheric N2O is a result of agricultural and other human activities that produce N2O that is isotopically lighter than the natural sources. For the Cape Grim archived air, the trends in δ15Nbulk, δ15Nα, δ15Nβ, and δ18O are -0.036±0.003, -0.028±0.022, - 0.038±0.022, and -0.023±0.006‰ yr-1, respectively, while those for the Law Dome firn air are -0.033±0.004, -0.031±0.014, -0.034±0.017, and -0.023±0.003‰ yr- 1, respectively. Although not statistically significant, there is a slightly larger negative trend in δ15Nβ versus that for δ15Nα15Nα and δ15Nβ trends among these archived air datasets is real atmospheric temporal and/or spatial variability is likely to have implications for the regional or global N2O isotope budgets, since box model results suggest that the relative trends in δ15Nα and δ15Nβ depend on the isotopic compositions of the natural and anthropogenic surface sources, as well as implications for constraining the relative contributions of nitrification and denitrification to the atmospheric N2O burden. In addition to the decreasing trends, time series analyses of the Cape Grim archived air demonstrate for the first time that small but statistically significant mean seasonal cycles in δ15Nbulk, δ15Nα, and δ18O can occur at the surface, quite remarkable for a trace gas with a 120-year lifetime. Box model simulations show the timing of these seasonal cycles is consistent with seasonally varying fluxes of N2O from the stratosphere, thermal outgassing from the ocean, and Southern Ocean ventilation. Interannual variations are also apparent at Cape Grim, particularly a large change in the amplitude of the seasonal cycles during the large ENSO in 1997-1998. Overall, these data provide important new constraints on the N2O budget and how N2O concentrations have changed on annual, interannual, and decadal time scales, and should thus contribute to a more detailed mechanistic understanding of what environmental variables control the biogeochemical cycling of atmospheric N2O.