Factors Influencing the Formation of Nitrous Acid from Photolysis of Particulate Nitrate

R. Sommariva*, M. S. Alam, L. R. Crilley, D. J. Rooney, W. J. Bloss, K. W. Fomba, S. T. Andersen, L. J. Carpenter

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review


Enhanced photolysis of particulate nitrate (pNO3) to form photolabile species, such as gas-phase nitrous acid (HONO), has been proposed as a potential mechanism to recycle nitrogen oxides (NOx) in the remote boundary layer (“renoxification”). This article presents a series of laboratory experiments aimed at investigating the parameters that control the photolysis of pNO3 and the efficiency of HONO production. Filters on which artificial or ambient particles had been sampled were exposed to the light of a solar simulator, and the formation of HONO was monitored under controlled laboratory conditions. The results indicate that the photolysis of pNO3 is enhanced, compared to the photolysis of gas-phase HNO3, at low pNO3 levels, with the enhancement factor reducing at higher pNO3 levels. The presence of cations (Na+) and halides (Cl-) and photosensitive organic compounds (imidazole) also enhance pNO3 photolysis, but other organic compounds such as oxalate and succinic acid have the opposite effect. The precise role of humidity in pNO3 photolysis remains unclear. While the efficiency of photolysis is enhanced in deliquescent particles compared to dry particles, some of the experimental results suggest that this may not be the case for supersaturated particles. These experiments suggest that both the composition and the humidity of particles control the enhancement of particulate nitrate photolysis, potentially explaining the variability in results among previous laboratory and field studies. HONO observations in the remote marine boundary layer can be explained by a simple box-model that includes the photolysis of pNO3, in line with the results presented here, although more experimental work is needed in order to derive a comprehensive parametrization of this process.

Original languageEnglish
Pages (from-to)9302-9310
Number of pages9
JournalJournal of Physical Chemistry A
Issue number44
Early online date25 Oct 2023
Publication statusPublished - 9 Nov 2023

Bibliographical note

Funding Information:
The authors thank Paul Williams (University of Manchester) and AMOF (Atmospheric Measurement and Observation Facility) for the loan of the SMPS instrument; Luis Neves (Cape Verde Atmospheric Observatory), Louisa Kramer (University of Birmingham), Mukesh Khare, Sanjay Kumar Gupta, Saif Khan, and Rulan Verma (Indian Institute of Technology Delhi) for their help during the Cape Verde and Delhi campaigns; and the University of Birmingham Biosciences workshop for their technical assistance. Funding was provided by the UK Natural Environment Research Council (grant numbers: NE/S000518/1 and NE/P016499/1).

Publisher Copyright:
© 2023 The Authors. Published by American Chemical Society.

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