Articles | Volume 16, issue 19
https://doi.org/10.5194/acp-16-12631-2016
https://doi.org/10.5194/acp-16-12631-2016
Research article
 | 
11 Oct 2016
Research article |  | 11 Oct 2016

Photochemical organonitrate formation in wet aerosols

Yong Bin Lim, Hwajin Kim, Jin Young Kim, and Barbara J. Turpin

Abstract. Water is the most abundant component of atmospheric fine aerosol. However, despite rapid progress, multiphase chemistry involving wet aerosols is still poorly understood. In this work, we report results from smog chamber photooxidation of glyoxal- and OH-containing ammonium sulfate or sulfuric acid particles in the presence of NOx and O3 at high and low relative humidity. Particles were analyzed using ultra-performance liquid chromatography coupled to quadrupole time-of-flight mass spectrometry (UPLC-Q-TOF-MS).

During the 3 h irradiation, OH oxidation products of glyoxal that are also produced in dilute aqueous solutions (e.g., oxalic acids and tartaric acids) were formed in both ammonium sulfate (AS) aerosols and sulfuric acid (SA) aerosols. However, the major products were organonitrogens (CHNO), organosulfates (CHOS), and organonitrogen sulfates (CHNOS). These were also the dominant products formed in the dark chamber, indicating non-radical formation. In the humid chamber (> 70 % relative humidity, RH), two main products for both AS and SA aerosols were organonitrates, which appeared at m ∕ z 147 and 226. They were formed in the aqueous phase via non-radical reactions of glyoxal and nitric acid, and their formation was enhanced by photochemistry because of the photochemical formation of nitric acid via reactions of peroxy radicals, NOx and OH during the irradiation.

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Short summary
We report that organonitrates were photochemically formed in wet aerosols via aqueous chemistry in the NOx–O3 chamber at high humidity. Organonitrates are considered to form in the gas phase (peroxy radical–NO during the daytime or VOC–NO3 during the nighttime); however, our chamber study results suggest daytime organonitrate formation in polluted and humid areas. Besides organonitrates, organonitrogens, organosulfates, and organonitrogen sulfates were also dominant photooxidation products.
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