Abstract
Particulate matter (PM) mass concentrations, seasonal cycles, source sector,
and source region contributions in Central Asia (CA) are analyzed for the
period April 2008–July 2009 using the Sulfur Transport and dEposition Model
(STEM) chemical transport model and modeled meteorology from the Weather
Research and Forecasting (WRF) model. Predicted aerosol optical depth (AOD)
values (annual mean value ~0.2) in CA vary seasonally, with
lowest values in the winter. Surface PM2.5 concentrations (annual mean
value ~10 μg m−3) also exhibit a seasonal cycle,
with peak values and largest variability in the spring/summer, and lowest
values and variability in the winter (hourly values from 2 to 90 μg m−3). Surface concentrations of black carbon (BC) (mean value
~0.1 μg m−3) show peak values in the winter. The
simulated values are compared to surface measurements of AOD as well as
PM2.5, PM10, BC, and organic carbon (OC) mass concentrations at two
regional sites in Kyrgyzstan (Lidar Station Teplokluchenka (LST)
and Bishkek). The predicted values of AOD and PM mass concentrations and
their seasonal cycles are fairly well captured. The carbonaceous aerosols
are underpredicted in winter, and analysis suggests that the winter heating
emissions are underestimated in the current inventory.
Dust, from sources within and outside CA, is a significant component of the
PM mass and drives the seasonal cycles of PM and AOD. On an annual basis,
the power and industrial sectors are found to be the most important
contributors to the anthropogenic portion of PM2.5. Residential
combustion and transportation are shown to be the most important sectors for
BC. Biomass burning within and outside the region also contributes to
elevated PM and BC concentrations. The analysis of the transport pathways
and the variations in particulate matter mass and composition in CA
demonstrates that this region is strategically located to characterize
regional and intercontinental transport of pollutants. Aerosols at these
sites are shown to reflect dust, biomass burning, and anthropogenic sources
from Europe; South, East, and Central Asia; and Russia depending on the time period.
Simulations for a reference 2030 emission scenario based on pollution
abatement measures already committed to in current legislation show that
PM2.5 and BC concentrations in the region increase, with BC growing
more than PM2.5 on a relative basis. This suggests that both the health
impacts and the climate warming associated with these particles may increase
over the next decades unless additional control measures are taken. The
importance of observations in CA to help characterize the changes that are
rapidly taking place in the region are discussed.