A24A-01 16:00h
Major Air Pollutants Over the Western Plain in Taiwan
The Western Plain of Taiwan where more than two thirds of Taiwan's 23 million population reside is practically a megacity. Oxidants and particulate matter at levels hazardous to human health are found throughout the Western Plain. In addition, deposition of large amounts of sulfate, nitrate, and ammonium ions has severely stressed the ecosystem. While emission controls have effectively brought down the concentrations of particulate matter in the last decade, ozone concentrations have increased significantly. The cause(s) of the ozone increase is not fully understood. Data taken by Taiwan EPA air quality stations suggest that smaller titration by nitrogen oxide in recent years is a contributor to the ozone increase in urban areas. There is some indication that an increase in synoptic scale background ozone concentration is also a contributor, implying a significant role of long-range transport.
A24A-02 16:15h
Measurements of Black Carbon Specific Absorption Made During the Mexico City Metropolitan Area Field Campaign of 2003
An important quantity used to characterize the effect of black carbon (BC) on aerosol absorption is the BC specific absorption, defined as the absorption cross section per unit mass. Using data taken as part of the Mexico City Metropolitan Area (MCMA) field campaign of 2003, we determine the specific absorption of BC. Mexico City is an ideal place to study aerosols and BC for many reasons, including large BC emissions, the high altitude of the site, which increases the relative importance of aerosols (over molecular scattering) in determining the radiative fluxes, and periods of both high and low relative humidity. The specific absorption is calculated in two ways; the first uses single scattering albedos derived from spectral irradiance measurements, while the other method uses LIDAR returns and surface measurements of BC. The value we find is steady from day to day, and close to its "canonical" value of about 10 m2/g. This suggests that BC is internally mixed with the ambient aerosol (or exists as very fine particles in an external mixture).
A24A-03 16:30h
Evidence of NO2 Contamination of Aerosol Single Scattering Albedo Retrievals Made During the MCMA Field Campaign of 2003
Solar irradiance data from the Multi-Filter Rotating Shadowband Radiometer (MFRSR) deployed during the MCMA field campaign were used to derive aerosol single scattering albedos (SSA) for five wavelengths spanning the near-UV (415 nm) to the near-IR (870 nm). Plotting these SSAs versus wavelength shows that the SSA at 415 nm is anomalously low. It is doubtful that this anomaly can be explained by aerosol optical properties, and we hypothesize that it is caused by the absorption of solar radiation by nitrogen dioxide (NO2) in near-UV spectral region. This absorption is usually small, because of the low background concentrations of NO2 in the atmosphere, and is therefore usually neglected. However, DOAS measurements of NO2 revealed that its concentration is so large in the Mexico City basin that NO2 absorption can no longer be ignored when retrieving SSAs. Accounting for this absorption in the retrieval increases the SSA at 415 nm to values which are plausible. This finding supports the hypothesis that large NO2 absorption is contaminating SSAs retrievals at 415 nm and one must therefore consider this absorption under certain circumstances.
A24A-04 16:45h
A New Fully Coupled Meteorology-Chemistry-Aerosol Model and Initial Results for Houston, Texas
Coupling of the Weather Research and Forecasting (WRF) version 2 regional meteorological model with the aerosol-chemistry mechanisms developed at Pacific Northwest National Laboratory is complete, and initial demonstration runs have been performed. WRF is the latest atmospheric sciences community model and the model framework enables advances in chemistry and aerosols to be tested and compared. This new model is well suited for simulating pollutants emitted from mega-cities through its ability to simultaneously simulate the local, regional, and synoptic impacts of aerosols. The aerosol-chemistry mechanisms that have been added are the Carbon Bond Mechanism-Zaveri photochemical (CBM-Z) module, the Model for Simulating Aerosol Interactions and Chemistry (MOSAIC) module, and the Fast-J photolysis module. These components are fully coupled and allow for on-line feedbacks between the meteorology, chemistry, aerosol, and radiative portions of the model. Aerosol feedbacks currently include the direct radiative effect, while the indirect effect of aerosols on clouds is under development and will be available at a future date. Mesh refinement, via nesting, allows higher resolution grids to be centered on areas with high emissions and strong gradients in atmospheric pollutants, whereas coarser outer nests can cover surrounding areas that are necessary for developing accurate meteorological conditions within the model as well as for determining long-range transport of trace gases and particulates. Demonstration runs have been performed, centered on Houston, Texas for the period 28 August through 2 September 2000. The simulated period corresponds with the 2000 Texas Air Quality Study (TexAQS) field campaign and thus has extensive meteorological, chemical, and aerosol measurements for verifying the model results. The domain configuration consists of three grids with horizontal grid spacings of 16, 4, and 1.33 km. Emission rates of trace gases and particulates are derived from the Texas Commission on Environmental Quality and from the Environmental Protection Agency?s National Emission Trend inventory. Results will be presented showing the radiative effect of the aerosol burden produced by the primary particulates released from the Houston metropolitan area on regional temperature distributions as well as an evaluation of the predicted concentration and spatial distribution
A24A-05 17:00h
Impact of biomass burning and biogenic emission on the evolution of Mexico City's air pollution plume
We use a newly developed regional chemical/transport model (WRF-Chem) to study the air pollutions in mega cities and their effect on surrounding areas. The model is based on a state of the art regional dynamical/transport model, the Weather Research Forecasting (WRF) model developed at NCAR in collaboration with other institutions. The model includes on-line calculation of dynamical inputs (winds, temperature, boundary layer, clouds etc.), transport (advective, diffusive, and convective), dry and wet deposition, gas phase chemistry, aerosol formation, radiation and photolysis rates, and surface emissions. The horizontal resolution of the model is flexible, ranging from a few km to several hundred km. In this study, we use a 6x6 km resolution located around Mexico City to study the air pollution inside the city and the impact of biomass burning and biogenic emissions on the chemical oxidants and ozone chemistry in the urban outflow plume. Mexico City is a highly polluted city, with NOx (NO2 + NO) and hydrocarbons (HCs) emissions resulting in locally high ozone concentrations (150-200 ppb peak values). The highly polluted city plume interacts strongly with the reactive emissions of the surrounding areas, esp. from vegetation and biomass burning. Biomass burning activity is highest in spring, and emits large amounts of NOx and CO. Vegetation emits a significant amount of HCs such as isoprene. After the city plume is transported into the surrounding areas, the polluted air is mixed with additional NOx and HCs emitted by biomass burning and vegetation. As a result, the ozone concentrations in the plume is significantly enhanced (20-30 %) at the far-end plume due to the NO emission of biomass burning, and is increased by 30-40 % at the near-end plume due to the biogenic emission of hydrocarbons.
A24A-06 17:12h
Intercontinental and Regional Modeling of Multiple Pollutants (Particulate Matter, Ozone, and Mercury) over the Pacific Regions
There is increasing evidence that air pollutants originating from regions outside of North America such as Asia could impact U.S. domestic air quality. At the same time, the U.S. is both an importer and exporter of air pollutants. A pioneer modeling project, the Intercontinental Transport and Climatic Effects of Air Pollutants (ICAP) project, has been undertaken at U.S EPA to help understand and assess these impacts associated with the intercontinental transport of air pollutants, including particulate matter (PM), ozone (O3), and mercury (Hg). The on-going modeling efforts include a series of modeling (108-km grid resolution) and emissions related activities over the pacific regions, including a 2001 Base year simulation, 2030 scenarios (IPCC's A1B and B2 scenarios), and several sensitivity studies (e.g., removal of man-made Asian emissions and North America emissions, etc.). The trans-Atlantic modeling effort has also been under way. The key modeling tool used in this project is the Models?3/Community Multi-scale Air Quality (CMAQ) modeling system developed at EPA. In addition, a related modeling effort has been undertaken to conduct model simulations over the East Asia (36-km grid) and an East China region (12-km grid). An expansion of this China modeling effort to urban fine-grid modeling (4-km grid) in Beijing and Shanghai has also been under way. The trans-Pacific modeling results revealed that PM 2.5 and O3 can be transported across the Pacific Ocean over a time period of 5 to 10 days before reaching North America and the U.S. A sensitivity study by removing the Asian man-made emissions showed that the impact of Asian man-made emissions on North America appeared to be persistent through the entire year, although exhibiting seasonal variations. The spring (April) had higher impact for PM 2.5, up to 2-2.5 ug/m3 (monthly average) in the western U.S. and up to 1-1.5 ug/m3 in the eastern U.S., while the summer (July) and spring (April) has comparable impacts for O3, up to 5-6 ppb (daily max) in the western U.S. and up to 2 ppb in the eastern U.S. The results of future scenarios modeling indicated that sustainable development (IPCC B1 case) will have significant improvement over the continued growth (IPCC A1B case) on the air quality across the Pacific regions.
A24A-07 17:24h
Regional/Urban Air Quality Modeling Assessment over China Using the Models-3/CMAQ System
China is the world's most populous country with a fast growing economy that surges in energy comsumption. It has become the second largest energy consumer after the United States although the per capita level is much lower than those found in developed or developing countries. Air pollution has become one of the most important problems of megacities such as Beijing and Shanghai and has serious impacts on public health, causes urban and regional haze. The Models-3/CMAQ modeling application that has been conducted to simulate multi-pollutants in China is presented. The modeling domains cover East Asia (36-kmx36-km) including Japan, South Korea, Korea DPR, Indonesia, Thailand, India and Mongolia, East China (12-kmx12-km) and Beijing/Tianjing, Shanghai (4-kmx4-km). For this study, the Asian emission inventory based on the emission estimates of the year 2000 that supported the NASA TRACE-P program is used. However, the TRACE-P emission inventory was developed for a different purpose such as global modeling. TRACE-P emission inventory may not be practical in urban area. There is no China national emission inventory available. Therefore, TRACE-P emission inventory is used on the East Asia and East China domains. The 8 districts of Beijing and Shanghai local emissions inventory are used to replace TRACE-P in 4-km domains. The meteorological data for the Models-3/CMAQ run are extracted from MM5. The model simulation is performed during the period January 1-20 and July 1-20, 2001 that presented the winter and summer time for China areas. The preliminary model results are shown O3 concentrations are in the range of 80 -120 ppb in the urban area. Lower urban O3 concentrations are shown in Beijing areas, possibly due to underestimation of urban man-made VOC emissions in the TRACE-P inventory and local inventory. High PM2.5 (70ug/m3 in summer and 150ug/m3 in winter) were simulated over metropolitan & downwind areas with significant secondary constituents. More comprehensive simulations in the Beijing, Shanghai areas are presented with sensitivity analysis. A comparison against available ozone and PM measurement data in Beijing, Shanghai is presented. The local emission inventory improvement in China is to be suggested to investigate. The modeling configuration of the Beijing 4-km x 4-km domain is to demonstrate the development of cost-effective control strategies for the air pollution control such as 2008 Olympic Game air quality management plan.
A24A-08 17:36h
Impacts of Black Carbon Aerosols on Photochemistry in Megacities
The impacts of black carbon (BC) aerosols on photolysis frequencies and ozone formation are assessed using regional chemical transport models (CTMs). Regional distributions of BC aerosols are calculated and compared with measurements of fine particle matter (PM2.5); the simulated daily mean BC aerosols are in good agreement with observations in urban sites. BC aerosols decrease the photolysis frequencies in the boundary layer. The ground level J[O3(1d)] and J[NO2] are decreased, leading to a decrease in the ground level ozone concentrations. Results related to two urban centers (Houston and Mexico City) will be presented. Our study demonstrates that the impacts of BC aerosols are nonnegligible in decreasing photolysis frequencies and ozone in polluted urban areas.
A24A-09 17:48h
Analysis of Potential Source Areas in MCMA-2003 using Concentration Fields Based on Modeled Back-trajectories
A meso-scale meteorological model (MM5) was used to forecast winds inside the Mexico City basin during the MCMA-2003 field campaign at high resolution. Backward and forward trajectories were calculated using the model FLEXTRA for an ensemble of particles arriving at the campaign supersite located at the National Center for Environmental Research and Training (CENICA) during the five-week time period. Residence time analysis showed short ventilation times inside the basin and only limited recirculation on certain days. This suggests that multi-day accumulation is not the main cause of high pollutant levels inside the basin. Backward trajectories were used to obtain concentration fields so as to identify possible source regions of measured pollutants. In order to verify the method this was applied to carbon monoxide, for which the emission sources are well characterized, at different monitoring sites. The method was then applied to sulfur dioxide and aerosol mass spectrometer measurements. This showed the importance of long-range transport for certain industrial sources and the predominance of emissions from the city center. Biogenic, volcanic and crustal emissions are also evaluated with their possible impact on pollutant levels in the city.