Characterization of secondary organic aerosol from heated-cooking-oil emissions: evolution in composition and volatility

Manpreet Takhar,Arthur W H Chan,Yunchun Li

doi:10.5194/acp-21-5137-2021

Abstract

Abstract. Cooking emissions account for a major fraction of urban organic aerosol. It is therefore important to understand the atmospheric evolution in the physical and chemical properties of organic compounds emitted from cooking activities. In this work, we investigate the formation of secondary organic aerosol (SOA) from oxidation of gas-phase organic compounds from heated cooking oil. The chemical composition of cooking SOA is analyzed using thermal desorption–gas chromatography–mass spectrometry (TD–GC–MS). While the particle-phase composition of SOA is a highly complex mixture, we adopt a new method to achieve molecular speciation of the SOA. All the GC-elutable material is classified by the constituent functional groups, allowing us to provide a molecular description of its chemical evolution upon oxidative aging. Our results demonstrate an increase in average oxidation state (from −0.6 to −0.24) and decrease in average carbon number (from 5.2 to 4.9) with increasing photochemical aging of cooking oil, suggesting that fragmentation reactions are key processes in the oxidative aging of cooking emissions within 2 d equivalent of ambient oxidant exposure. Moreover, we estimate that aldehyde precursors from cooking emissions account for a majority of the SOA formation and oxidation products. Overall, our results provide insights into the atmospheric evolution of cooking SOA, a majority of which is derived from gas-phase oxidation of aldehydes.

Highlights

Organic aerosol (OA) has important impacts on air quality, climate, and human health (Hallquist et al, 2009)
This difference suggests that the cooking organic aerosol (COA) factor resolved using positive matrix factorization (PMF) analysis is likely of primary origin and does not represent secondary organic aerosol (SOA) formed from atmospheric oxidation of cooking emissions
We show that cooking SOA occurring as a highly complex mixture can be deconvoluted using mass spectral fragmentation pattern to extract useful information about the chemical identities of organic compounds, such as functional groups and carbon number

Summary

Introduction

Organic aerosol (OA) has important impacts on air quality, climate, and human health (Hallquist et al, 2009). OA is often composed of thousands of organic compounds formed from a variety of sources. Particulate emissions from food cooking account for a significant fraction of OA (Allan et al, 2010; Crippa et al, 2013; Florou et al, 2017; Kostenidou et al, 2015; Lee et al, 2015; Mohr et al, 2012; Sun et al, 2011). Volatile organic compounds (VOCs) are emitted, and they can undergo oxidation and form secondary organic aerosol (SOA). Food cooking activities have substantial impacts on air quality in and downwind of urban areas

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