Air Pollutant Concentrations and Trends over the Eastern U.S. and China: Aircraft Measurements and Numerical Simulations

Abstract

In the last several decades, efforts have been made to mitigate air pollution all

around the world. With surface observations showing substantial decrease of criteria

pollutants, including O3, NOx, CO and SO2, the long-term aircraft measurements over

the eastern U.S. provide a unique opportunity to study the trend of the air pollutant

column contents and the regional transport in the free troposphere. Analyses of the

historical data indicated ~2.0 Dobson Unit/decade decrease in tropospheric O3

columns over the eastern U.S. with a similar decreasing trend of CO. The statistical

analysis also showed a significant decreasing trend for tropospheric SO2. Analyses of

the EPA CEMS emission data showed parallel reductions. A case study of

tropospheric O3 and SO2 over downwind area of Baltimore showed that the regional

transport by westerly wind from Ohio and Pennsylvania play an important role in the

local air quality issues.

As the second largest economy in the world, China's rapid economic growth

in the last decade lead to a dramatic increase in energy demand, which relied heavily

on coal burning. The enormous amount of SO2 emissions caused severe

environmental issues including acid deposition and particulate matter pollution. To

mitigate these air quality problems, strict control measures and regulations were

applied to abate sulfur emissions, especially before and during the 2008 Beijing

Olympics. Aircraft measurements of tropospheric SO2 were conducted over central

China in spring 2008, where intense measurements are lacking. A substantial amount

of SO2 was observed in the free troposphere, which is important to regional transport

and remote sensing. I successfully validated the SO2 columns with satellite retrievals,

and proved that the new OMI SO2 algorithm performs better than the conventional

algorithm. An emission inventory was evaluated through a combination of model

simulations and satellite products. Between 2006 and 2008, the SO2 emissions had

been reduced substantially over middle and eastern China. I also analyzed the model

simulations, and find the SO2 lifetime is ~ 38 h during spring in China and that ~50%

of Chinese emissions are exported to the western Pacific.