Seasonal and diurnal variations of atmospheric peroxyacetyl nitrate, peroxypropionyl nitrate, and carbon tetrachloride in Beijing

摘要

Atmospheric peroxyacetyl nitrate (PAN), peroxypropionyl nitrate (PPN), and carbon tetrachloride (CC1_4) were measured from September 2010 to August 2011 in Beijing. PAN exhibited low values from mid-autumn to early spring (October to March) with monthly average concentrations ranging from 0.28 to 0.73 ppbV, and increased from early spring to summer (March to August), ranging from 1.37-3.79 ppbV. The monthly variation of PPN was similar to PAN, with low values (below detection limit to 0.18 ppbV) from mid-autumn to early spring, and a monthly maximum in September (1.14 ppbV). The monthly variation of CCl_4 was tightly related to the variation of temperature, exhibiting a minimum in winter (69.3 pptV) and a maximum of 180.6 pptV in summer. Due to weak solar intensity and short duration, PAN and O_3 showed no distinct diurnal patterns from morning to night during winter, whereas for other seasons, they both exhibited maximal values in the late afternoon (ca. 15:00 to 16:00 local time) and minimal values during early morning and midnight. Good linear correlations between PAN and PPN were found in autumn (R = 0.91), spring (R = 0.94), and summer (R = 0.81), with slopes of 0.130, 0.222, and 0.133, respectively, suggesting that anthropogenic hydrocarbons dominated the photochemical formation of PANs in Beijing. Positive correlation between PAN and O_3 in summer with the low slopes (ΔO_3/ΔPAN) ranging from 9.92 to 18.0 indicated serious air pollution in Beijing, and strong negative correlation in winter reflected strong O_3 consumption by NO titration and less thermal decompositin of PAN.