Gaseous pollutants in Beijing urban area during the heating period 2007-2008: variability, sources, meteorological, and chemical impacts.

Gaseous pollutants, NO_y/NO_x, SO₂, CO, and O₃, were measured at an urban site in Beijing from 17 November 2007 to 15 March 2008. The average concentrations (with ±1σ) of NO_y, SO₂, CO, and O₃ were 29.0±2.7 ppb, 33.7±1.4 ppb, 62.7±4.0 ppb, 72.8±4.5 ppb, 1.99±0.13 ppm, 31.9±2.0 ppb, and 11.9±0.8 ppb, respectively, with hourly maxima of 200.7 ppb, 113.5 ppb, 303.9 ppb, 323.2 ppb, 15.06 ppm, 147.3 ppb, and 69.7 ppb, respectively. 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, SO₂, CO, and O₃ can all be decomposed in the two Lorentz curves, with their peak concentrations 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 O₃, 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 O₃, NO_x, and NO_y, ozone production efficiency (OPE) is estimated to be in the range of 0-8.9 (ppb ppb^-1) with the mean(±1σ) and median values being 1.1(±1.6) and 0.5 (ppb ppb^-1), respectively, for the winter 2007--2008 in Beijing. This low OPE would cause a photochemical O₃ source of 5 ppb day^-1, which is small but significant for surface O₃ in winter in Beijing. Downward transport of O₃-rich air from the free troposphere is the more important factor for the enhancement of the O₃ level in the surface layer, while high NO level for the destruction of O₃. The concentrations of SO₂, CO, and NO_x are 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, SO₂, and CO and empirical equations are obtained for the NO₃ 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 heating period, mobile sources in Beijing contribute more to NO_y than point sources. [ABSTRACT FROM AUTHOR]