Hygroscopicity and Volatility of Biomass Burning Aromatic and Nitroaromatic Compounds

Abstract

The microphysical characteristics of aerosol particles from biomass burning (BB) impact their behavior in the atmosphere. Aromatic and nitroaromatic species, either directly emitted or formed by oxidation, are commonly found in BB. Despite generally low hygroscopicity, the oxygen functionality in these compounds can give rise to limited interactions with water vapor, influencing the optical properties and phase of BB particles. Here, we report on a range of aromatic and nitroaromatic compounds, revealing varied hygroscopic growth across molecules with similar functionality, demonstrating the importance of specific molecular interactions in predicting hygroscopic growth and solubility. We show that 4-nitrocatechol, phthalic acid, and 2-, 3-, and 4-nitrophenol exhibit reversible interactions with water, while vanillic acid, syringic acid, p-hydroxybenzoic acid, and nitrobenzaldehyde are nonhygroscopic. Most components measured did not exhibit measurable evaporation over 2−3 h at 293 K, indicating vapor pressures <10 −5 Pa. The structural isomers of nitrophenol showed significant volatility that varied with molecular structure, RH, and particle phase. We report liquid-state vapor pressures from evaporation measurements of aqueous particles at high RH and solid-state vapor pressures from measurements under dry conditions. Overall, our findings offer crucial physicochemical insights into how BB compounds interact with water vapor and their implications for aerosol behavior.