Abstract
Peroxy acetyl nitrate (PAN) is an important photochemical product formed from the reactions between volatile organic compounds (VOCs) and nitrogen oxides (NOx) under sunlight. In this study, a field measurement was conducted at a rural site (the backgarden site, or BGS) of the Pearl River Delta (PRD) region in 2006, with the 10 min maximum PAN mixing ratios of 3.9 ppbv observed. The factors influencing the abundance of PAN at the BGS site was evaluated by the process analysis through the Weather Research and Forecasting-Community Multiscale Air Quality (WRF-CMAQ) model. The results suggested that the increase of PAN abundance at the BGS site was mainly controlled by the gas-phase chemistry, followed by vertical transport, while its loss was modulated mainly by dry deposition and horizontal transport. As the dominant important role of gas-phase chemistry, to provide detailed information on the photochemical formation of PAN, a photochemical box model with near-explicit chemical mechanism (i.e., the master chemical mechanism, MCM) was used to explore the relationship of photochemical PAN formation with its precursors based on the measured data at the BGS site. It was found that PAN formation was VOC-limited at the BGS site, with the oxidation of acetaldehyde the most important pathway for photochemical PAN production, followed by the oxidation and photolysis of methylglyoxal (MGLY). Among all the primary VOC precursors, isoprene and xylenes were the main contributors to PAN formation. Overall, our study provides new insights into the PAN photochemical formation and its controlling factors, and highlighted the importance of gas chemistry on the PAN abundance in the PRD region.
Highlights
Peroxy acetyl nitrate (PAN, CH3 C(O)O2 NO2 ) is a key photochemical pollutant which plays an important role in photochemistry and has detrimental effects on human and vegetation health [1].In addition to in situ formation near the emission sources of volatile organic compounds (VOCs) and Atmosphere 2018, 9, 372; doi:10.3390/atmos9100372 www.mdpi.com/journal/atmosphereAtmosphere 2018, 9, 372 nitrogen oxides (NOx ), PAN could be formed in air far away from these sources
PAN is formed from the reaction of NO2 and peroxy acetyl (PA) radical which is produced through photolysis and oxidation of a small number of oxygenated volatile organic compounds (OVOCs)
Note that the measurement data used in the present study were collected in 2006, which may not represent the present atmosphere of Pearl River Delta (PRD), where photochemical products (i.e., O3, PAN, and secondary organic aerosol (SOA)) and their precursors (VOCs and NOx ) have experienced significant variations in the last decade, because of the rapid urbanization/industrialization and considerable control measures implemented in the last decade [19,20]
Summary
Peroxy acetyl nitrate (PAN, CH3 C(O)O2 NO2 ) is a key photochemical pollutant which plays an important role in photochemistry and has detrimental effects on human and vegetation health [1]. Xue et al [9] investigated the PAN–precursor relationship at suburban and urban sites in Beijing, with an observation-based box model coupled with the Master Chemical Mechanism (MCM) They found that PAN formation is sensitive to both non-methane hydrocarbons (NMHCs) and NOx , with isoprene and aromatic NMHCs being the most important NMHC precursors, respectively, at suburban and urban sites. Note that the measurement data used in the present study were collected in 2006, which may not represent the present atmosphere of PRD, where photochemical products (i.e., O3 , PAN, and SOA) and their precursors (VOCs and NOx ) have experienced significant variations in the last decade, because of the rapid urbanization/industrialization and considerable control measures implemented in the last decade [19,20]. Region, and on the evaluation of the effective control measures for photochemical pollution in recent years in PRD [23]
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