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Peroxyacetic acid (PAA) is one of the most importantatmospheric organic peroxides, which have received increasing attention fortheir potential contribution to the oxidation capacity of the troposphereand the formation of secondary aerosols. We report here, for the first time,a series of data for atmospheric PAA concentrations at urban and ruralsites, from five field campaigns carried out in China in summer 2006, 2007and 2008. For these five measurements, daytime mean (08:00–20:00 LT) PAAconcentrations on sunlit days were 21.4–148.0 pptv with a maximum level of~1 ppbv. The various meteorological and chemical parametersinfluencing PAA concentrations were examined using Principal FactorAnalysis. This statistical analysis shows that the local photochemicalproduction was the major source of PAA, and its concentration increased withincreasing temperature, solar radiation and ozone but decreased withincreasing NOx (NO and NO2), CO, SO2, and relative humidity.Based on the dataset, several issues are highlighted in this study: (i)Because PAA is a product from the photochemical oxidation of some specificvolatile organic compounds (VOCs) that lead to acetyl peroxy radicals, theimportance of various VOCs with respect to the PAA formation is thereforeranked using the incremental reactivity method. (ii) The contribution of PANthermal degradation to PAA formation under conditions of different NOxconcentrations is estimated based on the chemical kinetics analysis. Theresult shows that PAN seems to play an important role in the formation ofPAA when the NO/NO2 concentration ratio was less than 0.2 and PAA wouldcorrespondingly have feedback on the PAN-NOx cycle. (iii) PAA and otherperoxides, such as methyl hydroperoxide (MHP) and H2O2, usuallyexhibited a similar asymmetric shape typically shifted to the afternoon.However, under some conditions, H2O2 diurnal cycle was out ofphase with MHP and PAA. The combination of linear regression and kineticsanalysis indicate that the formation and removal processes of H2O2may be different from those of MHP and PAA. (iv) Considering that PAA is thereservior of free radicals, its fate is expected to have an effect on thefree radical budget in the atmosphere. A box model based on the CBM-IVmechanism has been performed to access its influence on the radical budget.We suggest that the detailed information on PAA in the atmosphere is ofimportance to better understand the free radical chemistry

atmospheric chemistry and physics

Peroxyacetic acid in urban and rural atmosphere: concentration, feedback on PAN-NO&amp;lt;sub&amp;gt;x&amp;lt;/sub&amp;gt; cycle and implication on radical chemistry