Tropospheric air pollution modeling on a regional scale: Case studies for east and southeast Asia

East Asia has seen a phenomenal industrial growth in the past few decades resulting in significant increases in pollutant emissions. In this work, a 3-D regional-scale numerical investigation with the STEM - III model is carried out to explore and assess the environmental impacts of these tropospheric pollutants. Several case scenarios are studied to understand the influence of each on the tropospheric chemistry. A typical springtime episode (May 1987) is chosen during which maximum continental outflow occurs in east Asia.; Model simulations are performed to assess the relative importance of transport and chemical sources of tropospheric ozone. The model accurately captures most of the observed features in surface ozone. Ozone levels are strongly influenced by continental outflow of precursors and downward transport of ozone-rich air from the upper troposphere. Calculations for NMVOCs distribution give emission estimates of ethane, propane and ethene in east Asia ∼2.5, ∼2 and ∼7.5 Tg/yr respectively. Sensitivity analysis to increase in precursor emissions indicates ozone production over east Asia to be NO_x limited.; Transport calculations for mineral dust show two major dust events with levels exceeding 500 μg/m3 and a monthly net continental outflow of ∼6 Tg of dust. Gas/particle heterogeneous interactions are also considered. Particulate sulfate and nitrate, existing in the 4–5 μm diameter coarse mode, agree favorably with observations. 5–10% decrease in surface ozone is predicted closer to source regions of dust. HNO₃ /NO_x over marine boundary layer decreases by a factor 1–2 and >2 in the free troposphere due to aerosol processes.; Modeling forest fire impacts on the photochemical oxidant cycle in east Asia indicate a ∼30% increase in surface ozone close to the fire source. Consistent synoptic variability is obtained over source regions for calculated aerosol column loading and satellite data. Measurements during the Fall 1997 El Niño induced forest fires in southeast Asia show substantial ozone elevations in the middle and upper troposphere and decreases in the lower troposphere. Surface measurements indicate large aerosol increases (>500 μg/m 3). Numerical calculations show ozone partly originates from the upper troposphere and is also insitu produced chemically.