Temperature and volatile organic compound concentrations as controlling factors for chemical composition of &amp;lt;i&amp;gt;α&amp;lt;/i&amp;gt;-pinene-derived secondary organic aerosol

Louise N Jensen,Kasper Kristensen,Mikael Ehn,Lauriane L J Quéléver,Henrik B Pedersen,Ricky Teiwes,Marianne Glasius,Bernadette Rosati,Manjula R Canagaratna,Merete Bilde

doi:10.5194/acp-21-11545-2021

Abstract

Abstract. This work investigates the individual and combined effects of temperature and volatile organic compound precursor concentrations on the chemical composition of particles formed in the dark ozonolysis of α-pinene. All experiments were conducted in a 5 m3 Teflon chamber at an initial ozone concentration of 100 ppb and initial α-pinene concentrations of 10 and 50 ppb, respectively; at constant temperatures of 20, 0, or −15 ∘C; and at changing temperatures (ramps) from −15 to 20 and from 20 to −15 ∘C. The chemical composition of the particles was probed using a high-resolution time-of-flight aerosol mass spectrometer (HR-ToF-AMS). A four-factor solution of a positive matrix factorization (PMF) analysis of the combined HR-ToF-AMS data is presented. The PMF analysis and the elemental composition analysis of individual experiments show that secondary organic aerosol particles with the highest oxidation level are formed from the lowest initial α-pinene concentration (10 ppb) and at the highest temperature (20 ∘C). A higher initial α-pinene concentration (50 ppb) and/or lower temperature (0 or −15 ∘C) results in a lower oxidation level of the molecules contained in the particles. With respect to the carbon oxidation state, particles formed at 0 ∘C are more comparable to particles formed at −15 ∘C than to those formed at 20 ∘C. A remarkable observation is that changes in temperature during particle formation result in only minor changes in the elemental composition of the particles. Thus, the temperature at which aerosol particle formation is induced seems to be a critical parameter for the particle elemental composition. Comparison of the HR-ToF-AMS-derived estimates of the content of organic acids in the particles based on m/z 44 in the mass spectra show good agreement with results from off-line molecular analysis of particle filter samples collected from the same experiments. Higher temperatures are associated with a decrease in the absolute mass concentrations of organic acids (R-COOH) and organic acid functionalities (-COOH), while the organic acid functionalities account for an increasing fraction of the measured particle mass.

Highlights

Atmospheric aerosol particles can alter air quality (WHO, 2016) and visibility (Wang et al, 2009) on a regional scale
We present data from a subset of instruments involved in the ACCHA campaign: a temperature and humidity sensor (HC02-04) attached to a HygroFlex HF320 transmitter (Rotronic AG) placed in the center of the chamber; a scanning mobility particle sizer (SMPS), consisting of a differential mobility analyzer (DMA; TSI 3082) and a nano water-based condensation particle counter (CPC; TSI 3788); and a high-resolution time-of-flight aerosol mass spectrometer (HR-ToF-AMS; Aerodyne Research Inc.) (Jayne et al, 2000; DeCarlo et al, 2006; Canagaratna et al, 2007)
The positive matrix factorization (PMF) analysis revealed that the chemical composition of the Secondary organic aerosol (SOA) particles could be described by four factors, which differ in their dependence on volatile organic compounds (VOCs) concentration and experiment temperature

Summary

Introduction

Atmospheric aerosol particles can alter air quality (WHO, 2016) and visibility (Wang et al, 2009) on a regional scale. N. Jensen et al.: Impact of temperature and VOCs on the chemical composition of α-pinene-derived SOA tion products of volatile organic compounds (VOCs) emitted from both anthropogenic and biogenic sources (Sindelarova et al, 2014; Seinfeld and Pandis, 2016). ED(uOe3t)o, hydroxyl radicals (OH q), their low vapor pressures, some of the gas-phase oxidation products may partition onto already existing particles by condensation or reactive uptake and contribute to particle growth (Hallquist et al, 2009). Some low-vapor-pressure oxidation products of αpinene are able to nucleate (Kirkby et al, 2016) and likely play an important role in the initial growth of new particles in the atmosphere (O’Dowd et al, 2002; Riipinen et al, 2012; Ehn et al, 2014; Tröstl et al, 2016)

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