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

W. Lin, X. Xu, B. Ge, X. Liu
2011 Atmospheric Chemistry and Physics  
<p><strong>Abstract.</strong> Gaseous pollutants, NO<sub>y</sub>/NO<sub>x</sub>, SO<sub>2</sub>, CO, and O<sub>3</sub>, were measured at an urban site in Beijing from 17 November 2007 to 15 March 2008. The average concentrations (with &amp;plusmn; 1&amp;sigma;) of NO, NO<sub>2</sub>, NO<sub>x</sub>, NO<sub>y</sub>, CO, SO<sub>2</sub>, and O<sub>3</sub> were 29.0 &amp;plusmn; 2.7 ppb, 33.7 &amp;plusmn; 1.4 ppb, 62.7 &amp;plusmn; 4.0 ppb, 72.8 &amp;plusmn; 4.5 ppb, 1.99 &amp;plusmn; 0.13 ppm,
more » ... &amp;plusmn; 2.0 ppb, and 11.9 &amp;plusmn; 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<sub>y</sub>, SO<sub>2</sub>, CO, and O<sub>3</sub> 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<sub>x</sub>/NO<sub>y</sub> was 0.86 &amp;plusmn; 0.10, suggesting that the gaseous pollutants in Beijing in winter are mainly from local emissions. Data of O<sub>3</sub>, NO<sub>z</sub>, and NO<sub>x</sub>/NO<sub>y</sub> indicate that photochemistry can take place in Beijing even in the cold winter period. Based on the measurements of O<sub>3</sub>, NO<sub>x</sub>, and NO<sub>y</sub>, ozone production efficiency (OPE) is estimated to be in the range of 0–8.9 (ppb ppb<sup>−1</sup>) with the mean(&amp;plusmn; 1&amp;sigma;) and median values being 1.1(&amp;plusmn; 1.6) and 0.5 (ppb ppb<sup>−1</sup>), respectively, for the winter 2007–2008 in Beijing. This low OPE would cause a photochemical O<sub>3</sub> source of 5 ppb day<sup>−1</sup>, which is small but significant for surface O<sub>3</sub> in winter in Beijing. Downward transport of O<sub>3</sub>-rich air from the free troposphere is the more important factor for the enhancement of the O<sub>3</sub> level in the surface layer, while high NO level for the destruction of O<sub>3</sub>. The concentrations of SO<sub>2</sub>, CO, and NO<sub>x</sub> 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<sub>y</sub>, SO<sub>2</sub>, and CO and empirical equations are obtained for the NO<sub>y</sub> concentration. Based the equations, the relative contributions from mobile and point sources to NO<sub>y</sub> is estimated to be 66 &amp;plusmn; 30 % and 40 &amp;plusmn; 16 %, respectively, suggesting that even in the heating period, mobile sources in Beijing contribute more to NO<sub>y</sub> than point sources.</p>
doi:10.5194/acp-11-8157-2011 fatcat:lj2go6rmv5fzxn2r7orvjm3lni