Abstract

Abstract. Biogenic volatile organic compounds (BVOCs) are intensely emitted by forests and crops into the atmosphere. During the night, they react very rapidly with the nitrate radical (NO3), leading to the formation of a variety of functionalized products including organic nitrates and to large amounts of secondary organic aerosols (SOAs). Organic nitrates (ONs) have been shown not only to play a key role in the transport of reactive nitrogen and consequently in the ozone budget but also to be important components of the total organic-aerosol mass, while SOAs are known to play a direct and indirect role in the climate. However, the reactivity of BVOCs with NO3 remains poorly studied. The aim of this work is to provide new kinetic and mechanistic data for two monoterpenes (C10H16), α- and γ-terpinene, through experiments in simulation chambers. These two compounds, which have very similar chemical structures, have been chosen in order not only to overcome the lack of experimental data but also to highlight the influence of the chemical structure on the reactivity. Rate constants have been measured using both relative and absolute methods. They were found to be (1.2±0.5)×10-10 and (2.9±1.1)×10-11 cm3 molecule−1 s−1 for α- and γ-terpinene respectively. Mechanistic studies have also been conducted in order to identify and quantify the main reaction products. Total organic nitrate and SOA yields have been determined. While organic nitrate formation yields appear to be similar, SOA yields exhibit large differences with γ-terpinene being a much more efficient precursor of aerosols. In order to provide explanations for this difference, chemical analysis of the gas-phase products was performed at the molecular scale. Detected products allowed for proposing chemical mechanisms and providing explanations through peroxy and alkoxy reaction pathways.

Highlights

  • Since the early 1980s and the discovery of the nitrate radical (NO3) in the nocturnal troposphere (Noxon et al, 1980; Platt et al, 1980) and stratosphere (Naudet et al, 1981; Noxon et al, 1978), nighttime chemistry has been known to be active

  • Good linear tendencies are observed for the two reference compounds, and data obtained using PTR-Tof-MS and FTIR measurements are in good agreement

  • Because the results were in good agreement for both of the measurement techniques, linear regression was applied to all the values, leading to kγ -terpinene =

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Summary

Introduction

Since the early 1980s and the discovery of the nitrate radical (NO3) in the nocturnal troposphere (Noxon et al, 1980; Platt et al, 1980) and stratosphere (Naudet et al, 1981; Noxon et al, 1978), nighttime chemistry has been known to be active. During the night and during the day under low-sunlight conditions (e.g., in forest areas), NO3 has been shown to be an efficient oxidant, reacting with a large variety of volatile organic compounds (VOCs) including alkenes, aromatics and oxygenated VOCs (Atkinson and Arey, 2003). Most BVOCs have one or several C=C bonds and react rapidly with NO3 by addition of the oxidant onto the unsaturation(s) leading to lifetimes below a minute for the most reactive ones. This reaction leads to the formation of nitrooxy alkyl radicals which can evolve into organic nitrates (ONs). Organic nitrates have been shown to act as reservoirs for reactive nitrogen by undergoing long-range

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