Gaseous pollutants in Beijing: variability, sources, and impacts

Atmospheric Chemistry and Physics Discussions This discussion paper is/has been under review for the journal Atmospheric Chemistry and Physics (ACP). Please refer to the corresponding final paper in ACP if available. Abstract Gaseous pollutants, NO y /NO x , SO 2 , CO, and O 3 , were measured at an urban site The concentrations of the pollutants show " saw-toothed " patterns, which are attributable mainly to changes in wind direction and speed. The frequency distributions of the hourly mean concentrations of NO y , SO 2 , CO, and O 3 can all be decomposed in the two Lorentz curves, with their peak concentrations 10 representing background levels under different conditions. During the observation period , the average ratio NO x /NO y was 0.86±0.10, suggesting that the gaseous pollutants in Beijing in winter are mainly from local emissions. Data of O 3 , NO z , and NO x /NO y indicate that photochemistry can take place in Beijing even in the cold winter period. Based on the measurements of O 3 , NO x , and NO y , ozone production efficiency (OPE) 15 is estimated to be 0.76 for the winter 2007–2008 in Beijing. This low OPE would cause a photochemical O 3 source of 4 ppb/day, which is small but significant for surface O 3 in winter in Beijing. Downward transport of O 3-rich air from the free troposphere is the more important factor for the enhancement of the O 3 level in the surface layer, while high NO level for the destruction of O 3. The concentrations of SO 2 , CO, and NO x are 20 strongly correlated among each other, indicating that they are emitted by some common sources. Multiple linear regression analysis is applied to the concentrations of NO y , SO 2 , and CO and empirical equations are obtained for the NO y concentration. Based the equations, the relative contributions from mobile and point sources to NO y is estimated to be 66±30% and 40±16%, respectively, suggesting that even in the 25 heating period, mobile sources in Beijing contribute more to NO y than point sources.