Abstract
ABSTRACTSpringtime regional CO variability in the boundary layer and lower free troposphere in recent years has been studied by a combination of chemical transport models, satellite retrievals and surface-based measurements. Based upon the surface-level measurements and satellite observations, the CO mixing ratios and column densities downwind of the continental outflow were found to have significant reductions in the springtime of 2009 and 2010. Under the influence of continental outflow, there were 58% and 38% decreases in the monthly mean mixing ratios at a rural coastal site in March and April 2009–10, respectively, compared to the 2007–08 figure. Other than the global economic recession, the CO reductions downwind are attributed to the recent implementation of effective anthropogenic CO emissions control in China. The CO simulations by the MM5-CMAQ modeling system with fixed annual emissions support this argument. Features of frontal passage, including the higher CO mixing ratios in the post-frontal stage, were well-captured by the modeling system. The high-resolution nested-grid GEOS-Chem model was used to better characterize the downwind influences of CO due to the biomass burning in Southeast Asia in March and April 2008. The computed CO mixing ratios agreed well with satellite observations at 700 hPa during selected episodes when intense biomass burning activities in Southeast Asia were observed by the satellite images. The biomass-burning-derived CO provided a large contribution (33–86%) to the total CO mixing ratio in the lower free troposphere downwind over the South China Sea and western Pacific Ocean, based on the modeling results. Vertical export of CO in active convection events near the source region was evident.
Highlights
Carbon monoxide (CO) is an important tropospheric species which affects the oxidative capacity of the troposphere through its reaction with hydroxyl radicals
The springtime inter-annual variations of CO over the rural location Tap-Mun, Hong Kong and the continental outflow to the western Pacific based on CO column density measurements by satellite for the period
A decrease in surface CO at the measurement location and outflow region during 2009– 10 was found, which is attributed to the pollution control measures taken and global economic recession
Summary
Carbon monoxide (CO) is an important tropospheric species which affects the oxidative capacity of the troposphere through its reaction with hydroxyl radicals. Dramatic reductions of SO2 emissions were observed by the spaceborne Ozone Monitoring Instrument (OMI) in 2008 in several areas in northern China where large coalfired power plants operate. These reductions confirmed the effectiveness of the control measures (Li et al, 2010). Whether or not such control measures and technology improvements have effects upon remote areas through the outflow of CO is not established, and an update is urgently needed
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