Measurements of Peroxyacetyl Nitrate at a Background Site in the Pearl River Delta Region: Production Efficiency and Regional Transport

Abstract

Peroxyacetyl nitrate (PAN) is a trace constituent of the atmosphere but plays important roles in air pollution and atmospheric chemistry. To understand the chemical and transport processes of PAN in the Pearl River Delta (PRD) region, measurements of PAN, its precursors and related parameters were made at a regional background site in late summer and late autumn of 2011. Despite the fairly low ambient levels of PAN in general, several photochemical episodes with peak concentrations of PAN and ozone (O 3 ) as high as 4.86 and 189 ppbv were observed when the region was under influence of a tropical cyclone. PAN showed a seasonal variation with higher levels in autumn than in summer. PAN production efficiency, defined as the amount of PAN formed per unit amount of nitrogen oxides (NO x ) oxidized, was examined for the polluted PRD plumes, which indicated that PAN production accounted for on average approximately one third of the NO z formation. The photochemical production efficiency of PAN was much lower with respect to that of O 3 , suggesting that ~2.9 ppbv of PAN could be produced per formation of 100 ppbv of O 3 in the PRD plumes. Varying air masses including maritime air, regional air masses from the PRD, and continental outflow from eastern China were identified, which showed different chemical signatures in terms of both pollution levels and NO z budget. The highest abundances of PAN were measured in the PRD air masses, compared to the lowest concentrations in the marine air. Overall, the present study provides some new insights into the photochemical production and regional transport of PAN in the PRD region, where such investigations were very scarce before.

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

“…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. The variations of PAN levels in different field measurements were mainly related to the variations of its precursors.…”

“…Since PAN was first discovered in photochemical smog in Los Angeles in the 1950s, numerous studies have investigated the distribution and source contributions of PAN through field measurements and model simulations [3][4][5][6]. 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.…”

“…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.…”

Aerosol vertical distribution and optical properties over China from long-term satellite and ground-based remote sensing

“…For the Loess Plateau region, the data points are scattered from the lower left all the way to the upper right, because of mixed particles from anthropogenic pollution and natural dust. The data points in the Pearl River Delta show a similar scattered pattern but with a higher color ratio than those of anthropogenic pollution aerosols, because of the existence of a fraction (about 20 %) of larger-sized marine sea salt aerosols (Xu et al, 2015).…”

“…Also, the North China Plain contains anthropogenic dust year-round and transported natural dust in spring (Logan et al, 2013;. The air quality and pollution dispersal over the Pearl River Delta are controlled by specific meteorological conditions, and the Pearl River Delta aerosols are dominated by anthropogenic pollution and a small fraction of marine aerosols (Hara et al, 2011;Xu et al, 2015).…”