Effects of Anthropogenic Emissions on Secondary Organic Aerosol Formation from Biogenic Volatile Organic Compound

Abstract

Atmospheric secondary organic aerosols (SOA) can significantly affect air quality, climate, and human health. The formation of SOA is attributable to the vapour phase oxidation of biogenic or anthropogenic organic compounds and subsequent partitioning to the particulate phase. The oxidation of biogenic volatile organic compounds (bVOCs), such as monoterpenes, has received extensive attention owing to their larger global emissions compared with anthropogenic volatile organic compounds (aVOCs). α-Pinene, constituting nearly 50% of the global monoterpene emissions and with a high SOA forming efficiency is thereby considered one of the most important SOA precursors in the atmosphere. The essential characteristics of α-pinene SOA, such as the oxidation pathways, molecular constitutions, volatility, and yields, have been widely studied in chamber experiments. However, most of them focused on single precursor systems. In the real atmosphere, SOA formation is influenced by the interactions of other molecules. Human emissions, such as the aVOCs, NOx, and CO, are likely to affect α-pinene SOA formation processes. Thus, the chamber investigation on SOA formation should be considered more realistically. Establishing a framework to understand the interactions of mixed SOA precursors in the presence of NOx and CO is needed. Diesel vehicular emission is an important anthropogenic source for SOA precursors in urban areas. n-Dodecane (C12H26) represents a reasonable proxy for intermediate volatility organic compounds (IVOC) in diesel exhaust. In this study, we plan to investigate the SOA formation from (i) α-pinene and n-dodecane system and (ii) α-pinene and diesel exhaust system, under controlled NOx and CO conditions. The experiments are conducted at the Manchester Aerosol Chamber (MAC) facility, which is an 18 m3 fluorinated ethylene propylene bag. A combination of gas-phase and particle-phase analytical instruments are employed for the experiments: High-Resolution Time-of-Flight Chemical Ionization Mass Spectrometer with a Filter Inlet for Gases and Aerosols (FIGAERO-CIMS) equipped with iodide reagent, Proton-transfer-reaction Time-of-Flight Mass Spectrometry (PTR-ToF-MS), Differential Mobility Particle Sizer (DMPS), Compact Time-of-Flight Aerosol Mass Spectrometer (C-ToF-AMS), and Gas Analysers. This work reports the changes in SOA compositions, SOA particle volatility, and yields in the mixtures of α-pinene and n-dodecane/diesel exhaust under controlled NOx and CO conditions. The results provide new insights into SOA formation in mixtures.