Molecular corridors and parameterizations of volatility in the chemical evolution of organic aerosols

Ying Li,Manabu Shiraiwa,Ulrich Pöschl

doi:10.5194/acp-16-3327-2016

Abstract

Abstract. The formation and aging of organic aerosols (OA) proceed through multiple steps of chemical reaction and mass transport in the gas and particle phases, which is challenging for the interpretation of field measurements and laboratory experiments as well as accurate representation of OA evolution in atmospheric aerosol models. Based on data from over 30 000 compounds, we show that organic compounds with a wide variety of functional groups fall into molecular corridors, characterized by a tight inverse correlation between molar mass and volatility. We developed parameterizations to predict the saturation mass concentration of organic compounds containing oxygen, nitrogen, and sulfur from the elemental composition that can be measured by soft-ionization high-resolution mass spectrometry. Field measurement data from new particle formation events, biomass burning, cloud/fog processing, and indoor environments were mapped into molecular corridors to characterize the chemical nature of the observed OA components. We found that less-oxidized indoor OA are constrained to a corridor of low molar mass and high volatility, whereas highly oxygenated compounds in atmospheric water extend to high molar mass and low volatility. Among the nitrogen- and sulfur-containing compounds identified in atmospheric aerosols, amines tend to exhibit low molar mass and high volatility, whereas organonitrates and organosulfates follow high O : C corridors extending to high molar mass and low volatility. We suggest that the consideration of molar mass and molecular corridors can help to constrain volatility and particle-phase state in the modeling of OA particularly for nitrogen- and sulfur-containing compounds.

Highlights

Organic aerosols (OA) consist of a myriad of chemical species and account for a substantial mass fraction (20–90 %) of the total submicron particles in the troposphere (Jimenez et al, 2009; Nizkorodov et al, 2011)
More than 80 % of the CHON and CHOS compounds are located in the range covered from intermediate volatility OC (IVOC) to low-volatile OC (LVOC), and about 10 % of them belong to the extremely low-volatile OC (ELVOC) group
The locations of organic compounds observed in the Cosmics Leaving Outdoor Droplets (CLOUD) experiments (Fig. 5a) and at Hyytiälä (Fig. 5b) in the molecular corridor are similar by occupying the space close to the sugar alcohol line, indicating that chemical properties of these organic compounds are similar and chamber experiments represent ambient observations well

Summary

Introduction

Organic aerosols (OA) consist of a myriad of chemical species and account for a substantial mass fraction (20–90 %) of the total submicron particles in the troposphere (Jimenez et al, 2009; Nizkorodov et al, 2011). Where M is the molar mass (g mol−1), p0 is the saturation vapor pressure (mm Hg), R is the ideal gas constant (8.205 × 10−5 atm K−1 mol−1 m3), and T is the temperature (K) We classified these organic compounds into six classes based on chemical composition: CH, CHO, CHN, CHON, CHOS, and CHONS, with the number of compounds of 328, 8420, 2968, 13 628, 925, and 3367, respectively. Applying the newly developed saturation mass concentration estimation method to laboratory experiments and field campaigns, the observed organic compounds were mapped into the molecular corridor with an alternative representation displaying C0 as a function of molar mass, which appears more straightforward for direct comparisons to mass spectra (Shiraiwa et al, 2014). These large data sets provide insights into the chemical and physical nature of OA from different sources and their evolution upon chemical transformation

CH and CHO compounds

Nitrogen- and sulfur-containing compounds

Findings

Summary and conclusions