Peroxyacetic acid in urban and rural atmosphere: concentration, feedback on PAN-NOx cycle and implication on radical chemistry State Key Laboratory of Environmental Simulation and Pollution Control, College of Environmental Sciences and Engineering, Peking University, Beijing 100871, China
Received: 02 Oct 2009 – Published in Atmos. Chem. Phys. Discuss.: 26 Oct 2009 Abstract. Peroxyacetic acid (PAA) is one of the most important
atmospheric organic peroxides, which have received increasing attention for
their potential contribution to the oxidation capacity of the troposphere
and the formation of secondary aerosols. We report here, for the first time,
a series of data for atmospheric PAA concentrations at urban and rural
sites, from five field campaigns carried out in China in summer 2006, 2007
and 2008. For these five measurements, daytime mean (08:00–20:00 LT) PAA
concentrations on sunlit days were 21.4–148.0 pptv with a maximum level of
~1 ppbv. The various meteorological and chemical parameters
influencing PAA concentrations were examined using Principal Factor
Analysis. This statistical analysis shows that the local photochemical
production was the major source of PAA, and its concentration increased with
increasing temperature, solar radiation and ozone but decreased with
increasing 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 specific
volatile organic compounds (VOCs) that lead to acetyl peroxy radicals, the
importance of various VOCs with respect to the PAA formation is therefore
ranked using the incremental reactivity method. (ii) The contribution of PAN
thermal degradation to PAA formation under conditions of different NOx
concentrations is estimated based on the chemical kinetics analysis. The
result shows that PAN seems to play an important role in the formation of
PAA when the NO/NO2 concentration ratio was less than 0.2 and PAA would
correspondingly have feedback on the PAN-NOx cycle. (iii) PAA and other
peroxides, such as methyl hydroperoxide (MHP) and H2O2, usually
exhibited a similar asymmetric shape typically shifted to the afternoon.
However, under some conditions, H2O2 diurnal cycle was out of
phase with MHP and PAA. The combination of linear regression and kinetics
analysis indicate that the formation and removal processes of H2O2
may be different from those of MHP and PAA. (iv) Considering that PAA is the
reservior of free radicals, its fate is expected to have an effect on the
free radical budget in the atmosphere. A box model based on the CBM-IV
mechanism has been performed to access its influence on the radical budget.
We suggest that the detailed information on PAA in the atmosphere is of
importance to better understand the free radical chemistry.
Revised: 06 Jan 2010 – Accepted: 08 Jan 2010 – Published: 25 Jan 2010
Citation: Zhang, X., Chen, Z. M., He, S. Z., Hua, W., Zhao, Y., and Li, J. L.: Peroxyacetic acid in urban and rural atmosphere: concentration, feedback on PAN-NOx cycle and implication on radical chemistry, Atmos. Chem. Phys., 10, 737-748, doi:10.5194/acp-10-737-2010, 2010.