Summertime distributions of peroxyacetyl nitrate (PAN) and peroxypropionyl nitrate (PPN) in Beijing: Understanding the sources and major sink of PAN

Abstract

a b s t r a c tPeroxyacetyl nitrate (PAN), a major secondary pollutant in the atmosphere, has received much concern for its particular importance in atmospheric chemistry and adverse effects on human and plants. Atmospheric PAN and PPN were measured by using a gas chromatograph equipped with electron capture detector (GC-ECD) from June to September 2010, and the source and major sink for PAN were firstly studied in Beijing. The distinct diurnal variations of PAN and PPN with maximum in the afternoon were observed, and the mean and maximum values were 2.61 ± 2.57 ppbv (N ¼ 839) and 12.5 ppbv for PAN and 0.52 ± 0.38 ppbv (N ¼ 152) and 2.16 ppbv for PPN during the measuring period, respectively. Good correlation (R ¼ 0.85) between PAN and PPN with a slope (DPPN/DPAN) of 0.134 indicated that anthropogenic volatile organic compounds (AVOCs) dominated the photochemical formation of PANs in Beijing. Further, we found acetaldehyde was the predominant carbonyl precursor of PAN with the contribution of 59.7% to the total peroxyacetyl (PA) radical. Methyl glyoxal, methacrolein, acetone, methyl vinyl ketone, and biacetyl contributed 7.1%, 8.8%, 19.7%, 3.4%, and 1.3% to total PA radical, respectively. Anti-correlation between PAN concentrations and the NO/NO 2 ratios was found during the whole investigating period. In addition, the amount of PAN lost by thermal decomposition (TPAN) accounted for remarkable fractions of PAN observed under high temperature during both daytime and nighttime.

PAN–Precursor Relationship and Process Analysis of PAN Variations in the Pearl River Delta Region

“…Figure 8 shows three major pathways leading to production of PA radical at the BGS site during the sampling period, in the following order: the oxidation of acetaldehyde by OH and NO 3 (46 ± 5%), photolysis and oxidation of methylglyoxal (MGLY) by OH and NO 3 (31 ± 2%), and radical recycling of other radicals to the PA radical (21 ± 1%). Our results were consistent with those simulated at suburban and urban sites in Beijing [9,13]. The remaining pathway for production of PA radical was very minor (about 2%), contributed to from the oxidation of other OVOCs and MPAN (methacryloyl peroxy nitrate, a secondary product formed through the acylperoxy radical (MACO 3 ) with NO 2 ).…”

“…In general, the median mixing ratio of PAN at the BGS site was 0.31 ± 0.02 ppbv, with the maximum and the average value of daily maximum mixing ratio of 3.9 and 1.3 ppbv, respectively. These levels were lower than those measured at urban and suburban areas in Beijing [8,9,13], and an urban site in Lanzhou in western China [7]. Compared to other field measurements in the PRD region, the mixing ratios of PAN at the BGS site were lower than those observed at the regional background site (the Hok Tsui site, measurement in 2011) [12] and the downwind rural site in the PRD region (the Heshan site, measurement in 2012) [18], which were mainly influenced by the outflow air masses from the center PRD region.…”

“…It was found that the rate of the thermal decomposition of PAN could increase by~29% if the temperature was increased by 5 • C (data not shown). On the other hand, though variations in mixing ratios of precursors could result in the different production rates of PAN between urban and rural areas, the deviation between the production rate of PAN and its destruction rate through thermal decomposition, could be smaller at urban areas due to higher temperatures in urban areas [13]. Indeed, through the simulation of the PBM-MCM model, it was found that the deviation between the production rate and destruction rate was about 41 pptv/h at the urban site, lower than those simulated at the rural site (p < 0.01).…”

“…The characterization includes the abundance of PAN, the relationship with its precursors, and the contributions of regional transport in different environments.The spatial variations of PAN and its formation mechanism has also been investigated in China, including urban, suburban, rural, and remote areas, for example, in Lanzhou [7],, and in the Pearl River Delta (PRD) region [11,12]. Zhang et al [13] found that the thermal decomposition dominated PAN removal in urban environments in Beijing, from June to September 2010. Liu et al [8] investigated the contribution of different precursors to the photochemical PAN formation with the Regional Chemical and Transport Model (REAM), and found that photooxidation of aromatic non-methane hydrocarbons (NMHCs) was the dominant PAN source at the Peking University (PKU) site.…”

Secondary product creation potential (SPCP): a metric for assessing the potential impact of indoor air pollution on human health

“…16 There are also numerous health effects associated with exposure to PAN type species, given they behave as mutagens, phytotoxins and lachrymators. 35 Finally, deposition of organic nitrates into the lung lining uid may produce nitric acid following hydrolysis, leading to reductions in pulmonary function. 36 For the model runs described here, the sum of the mixing ratios of the secondary products is divided by 10 (b ¼ 10 as we added 10 ppb of each VOC for the model runs), so that the SPCP is a measure of the mixing ratio in ppb of 'potentially harmful secondary products (SP)' formed per ppb of VOC added to an indoor environment (or ppb SP/ppb VOC).…”