Carbonaceous aerosols over China-review of observations, emissions, and climate forcing

Carbonaceous aerosols have been attracting attention due to the influence on visibility, air quality, and regional climate. Statistical analyses based on concentration levels, spatial-temporal variations, correlations, and organic carbon (OC) to element carbon (EC) ratios from published data of OC and EC in particulate matter (PM2.5 and PM10) were carried out in order to give a carbonaceous aerosol profile in China. The results showed maxima for OC of 29.5 +/- 18.2 mu g C m(-3) and for EC of 8.4 +/- 6.3 mu g C m(-3) in winter and minima for OC of 12.9 +/- 7.7 mu g C m(-3) in summer and for EC of 4.6 +/- 2.8 mu g C m(-3) in spring. In addition, OC and EC both had higher concentrations in urban than those in rural sites. Carbonaceous aerosol levels in China are about three to seven times higher compared to those in the USA and Europe. OC and EC occupied 20 +/- 6 and 7 +/- 3 % of PM2.5 mass and 17 +/- 7 and 5 +/- 3 % of PM10 mass, respectively, implying that carbonaceous aerosols are the main component of PM, especially OC. Secondary organic carbon (SOC) was a significant portion of PM and contributed 41 +/- 26 % to OC and 8 +/- 6 % to PM2.5 mass. The OC/EC ratio was 3.63 +/- 1.73, which, along with the good correlation between OC and EC and the OC to EC slope of 2.29, signifies that coal combustion and/or vehicular exhaust is the dominated carbonaceous aerosol source in China. These provide a primary observation-based understanding of carbonaceous aerosol pollution in China and have a great significance in improving the emission inventory and climate forcing evaluation.