Nitrate radicals and biogenic volatile organic compounds: oxidation, mechanisms, and organic aerosol

Abstract

Oxidation of biogenic volatile organic compounds (BVOC) by the nitrate radical (NO3) represents one of the important interactions between anthropogenic emissions related to combustion and natural emissions from the biosphere. This interaction has been recognized for more than 3 decades, during which time a large body of research has emerged from laboratory, field, and modeling studies. NO3-BVOC reactions influence air quality, climate and visibility through regional and global budgets for reactive nitrogen (particularly organic nitrates), ozone, and organic aerosol. Despite its long history of research and the significance of this topic in atmospheric chemistry, a number of important uncertainties remain. These include an incomplete understanding of the rates, mechanisms, and organic aerosol yields for NO3-BVOC reactions, lack of constraints on the role of heterogeneous oxidative processes associated with the NO3 radical, the difficulty of characterizing the spatial distributions of BVOC and NO3 within the poorly mixed nocturnal atmosphere, and the challenge of constructing appropriate boundary layer schemes and non-photochemical mechanisms for use in state-of-the-art chemical transport and chemistry–climate models.This review is the result of a workshop of the same title held at the Georgia Institute of Technology in June 2015. The first half of the review summarizes the current literature on NO3-BVOC chemistry, with a particular focus on recent advances in instrumentation and models, and in organic nitrate and secondary organic aerosol (SOA) formation chemistry. Building on this current understanding, the second half of the review outlines impacts of NO3-BVOC chemistry on air quality and climate, and suggests critical research needs to better constrain this interaction to improve the predictive capabilities of atmospheric models.

Observational assessment of the role of nocturnal residual-layer chemistry in determining daytime surface particulate nitrate concentrations

“…The nitrate reactivity towards each VOC is calculated as k VOC + NO 3 · [VOC], where the k VOC + NO 3 is the VOC-specific rate coefficient and [VOC] is the VOC concentration (Ng et al, 2017). Average afternoon VOC concentrations are used, which should be representative of the initial concentrations in the RL.…”

Direct measurement of NO<sub>3</sub> reactivity in a boreal forest

“…To a first approximation we can assume that, at nighttime, in the absence of NO and sunlight, each NO 3 radical formed in the reaction of NO 2 with O 3 will react with a biogenic hydrocarbon, 10 resulting in formation of an organic nitrate at a yield of between 20 and 100%, depending on the identity of the organic reactant (Ng et al, 2017). The large values for k OTG obtained during the day means that a significant fraction of the NO 3 formed can be converted to organic nitrates rather than result in re-formation of NO 2 via reaction with NO or photolysis.…”

The role of highly oxygenated molecules (HOMs) in determining the composition of ambient ions in the boreal forest

“…Different reaction pathways leading to ON formation have been proposed. Due to their low vapour pressures, ONs are also expected to have a potentially important role in the formation and growth of secondary organic aerosol (SOA; Farmer et al, 2010;Kiendler-Scharr et al, 2016;Lee et al, 2016;Ng et al, 2017). In addition, Kulmala et al (2013) recently proposed that the organonitrate C 10 H 15 O 5 NO 3 is important player in NPF and Jokinen et al (2017) confirmed that the abundance of ONs during solar eclipse correlates with clustering.…”