Biogenic and anthropogenic sources of isoprene and monoterpenes and their secondary organic aerosol in Delhi, India

[摘要] Isoprene and monoterpene emissions to the atmosphere are generallydominated by biogenic sources. The oxidation of these compounds can lead tothe production of secondary organic aerosol; however the impact of thischemistry in polluted urban settings has been poorly studied. Isoprene andmonoterpenes can form secondary organic aerosol (SOA) heterogeneously via anthropogenic–biogenicinteractions, resulting in the formation of organosulfate (OS) andnitrooxy-organosulfate (NOS) species. Delhi, India, is one of the most pollutedcities in the world, but little is known about the emissions of biogenicvolatile organic compounds (VOCs) or the sources of SOA. As part of the DELHI-FLUX project, gas-phasemixing ratios of isoprene and speciated monoterpenes were measured duringpre- and post-monsoon measurement campaigns in central Delhi. Nocturnalmixing ratios of the VOCs were substantially higher during the post-monsoon(isoprene: ( 0.65±0.43 ) ppbv; limonene: ( 0.59±0.11 ) ppbv; α -pinene: ( 0.13±0.12 ) ppbv) than the pre-monsoon (isoprene:( 0.13±0.18 ) ppbv; limonene: 0.011±0.025 (ppbv); α -pinene: 0.033±0.009 ) period. At night, isoprene and monoterpeneconcentrations correlated strongly with CO during the post-monsoonperiod. Filter samples of particulate matter less than 2.5  µm indiameter (PM 2.5 ) were collected and the OS and NOS content analysedusing ultra-high-performance liquid chromatography tandem mass spectrometry(UHPLC-MS 2 ). Inorganic sulfate was shown to facilitate the formation ofisoprene OS species across both campaigns. Sulfate contained within OS andNOS species was shown to contribute significantly to the sulfate signalmeasured via AMS. Strong nocturnal enhancements of NOS species were observedacross both campaigns. The total concentration of OS and NOS species contributedan average of ( 2.0±0.9 ) % and ( 1.8±1.4 ) % to the totaloxidized organic aerosol and up to a maximum of 4.2 % and 6.6 %across the pre- and post-monsoon periods, respectively. Overall, this studyprovides the first molecular-level measurements of SOA derived from isopreneand monoterpene in Delhi and demonstrates that both biogenic andanthropogenic sources of these compounds can be important in urban areas.

[学科分类] 医学（综合）