Volatility of Cl-Initiated C₁₂–C₁₄ <i>n</i>‑Alkylcyclohexane Secondary Organic Aerosol: Effects of NO_<i>x</i> and Photoaging

Abstract

Long-chain alkanes are important components of intermediate-volatility organic compounds, especially for C12–C14 cyclic compounds. In this study, we focus on the volatilities of C12–C14 n-alkylcyclohexane secondary organic aerosol (SOA) initiated by Cl atoms and investigate the influence of NOx, aging time, precursors, and SOA mass loading. Dilution and precursors seem to have little effect on the SOA volatility. Low-volatility organic compounds (LVOCs) account for a dominant part of SOA volatility distribution. Due to the presence of NOx, more fractions of extremely low-volatility OCs (ELVOCs) and a higher carbon oxidation state (OS̅C) result in a decrease in the SOA volatility. During the aging period, the fraction of ELVOCs increased, and semi-volatile organic compounds (SVOCs) decreased simultaneously. Even after 9 h of photoaging, the particle fractions of ELVOCs exceeded those of SVOCs to be the second largest part following LVOCs under high-NOx conditions. The particle-phase oligomerization is the dominant way that influenced the SOA volatility during the photoaging period, according to the product analysis. This study emphasizes the importance of Cl-initiated alkane SOA in the polluted region with high NOx levels