Organosulfates from Pinene and Isoprene over the Pearl River Delta, South China: Seasonal Variation and Implication in Formation Mechanisms

Abstract

Biogenic organosulfates (OSs) are important markers of secondary organic aerosol (SOA) formation involving cross reactions of biogenic precursors (terpenoids) with anthropogenic pollutants. Until now, there has been rare information about biogenic OSs in the air of highly polluted areas. In this study, fine particle (PM 2.5 ) samples were separately collected in daytime and nighttime from summer to fall 2010 at a site in the central Pearl River Delta (PRD), South China. Pinene-derived nitrooxyorganosulfates (pNOSs) and isoprene-derived OSs (iOSs) were quantified using a liquid chromatograph (LC) coupled with a tandem mass spectrometer (MS/MS) operated in negative electrospray ionization (ESI) mode. The pNOSs with MW 295 exhibited higher levels in fall (151 ± 86.9 ng m −3 ) than summer (52.4 ± 34.0 ng m −3 ), probably owing to the elevated levels of NOx and sulfate in fall when air masses mainly passed through city clusters in the PRD and biomass burning was enhanced. In contrast to observations elsewhere where higher levels occurred at nighttime, pNOS levels in the PRD were higher during the daytime in both seasons, indicating that pNOS formation was likely driven by photochemistry over the PRD. This conclusion is supported by several lines of evidence: the specific pNOS which could be formed through both daytime photochemistry and nighttime NO 3 chemistry exhibited no day− night variation in abundance relative to other pNOS isomers; the production of the hydroxynitrate that is the key precursor for this specific pNOS was found to be significant through photochemistry but negligible through NO 3 chemistry based on the mechanisms in the Master Chemical Mechanism (MCM). For iOSs, 2-methyltetrol sulfate ester which could be formed from isoprene-derived epoxydiols (IEPOX) under low-NOx conditions showed low concentrations (below the detection limit to 2.09 ng m −3 ), largely due to the depression of IEPOX formation by the high NOx levels over the PRD. ■ INTRODUCTIONBiogenic volatile organic compounds (BVOCs) including isoprene and monoterpenes 1 contribute significantly to the global secondary organic aerosol (SOA) budget. 2 Recent studies have shown that the conversion of BVOCs to SOA can be significantly promoted in the presence of high anthropogenic emissions. 3−6 As notable SOA products of BVOCs reacting with anthropogenic pollutants under acidic conditions, organosulfates (OSs) have been detected in both laboratory-generated SOA 7−10 and ambient aerosols. 11−18 Moreover, OSs could contribute a significant fraction of fine particles, accounting for up to 30% of organic matter (OM) 9,19−23 and up to 10% of total sulfate. 24,25 The formation mechanisms of OSs are still unclear. Previous chamber studies have demonstrated that both OH-photooxidation and NO 3 dark reactions can form pinene-derived nitrooxy-organosulfates (pNOSs) on acidic particles. 9 The pNOSs were only detected in nighttime samples in northeastern Bavaria, Germany, suggesting a role for nighttime NO 3 chemistry in pNOS formation. 15 How...

Wet and Dry Nitrogen Depositions in the Pearl River Delta, South China: Observations at Three Typical Sites With an Emphasis on Water‐Soluble Organic Nitrogen

“…Therefore, the ratio of K + /WSOC in the atmosphere is expected to be higher when biomass burning occurs (Wang et al, ). We found that in wet deposition K + /WSOC ratio showed higher level during fall in both years, even at the urban GIG site (Figure ), indicating an enhanced biomass burning during the period (He et al, ). K + might be also derived from soil dust, sea salt, or biogenic emission (Artaxo et al, ; Chen et al, ).…”

“…WQS (113°55′E, 22°71′N), a small town located in south of Guangzhou, is a background site of the PRD with few textile and clothing workshops. WQS is mainly affected by regionally transported pollutants from surrounding cities (He et al, ), especially in dry season (October to March of next year). In wet season, air masses from the South China Sea can dilute the air pollutants at this site.…”

Attributing risk burden of PM2.5-bound polycyclic aromatic hydrocarbons to major emission sources: Case study in Guangzhou, south China

“…In summer, the south wind dominated and brought clean oceanic air from the South China Sea and southeast coast, whereas in winter air masses mainly from the west and the northwest brought pollutants from mainland ( Fig. S1) (He et al, 2014). Relatively higher temperature, humidity and wind speed in summer also led to stronger photolysis and dispersion of PAHs (Yang et al, 2010).…”

A two-dimensional volatility basis set – Part 3: Prognostic modeling and NO<sub><i>x</i></sub> dependence

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