Release of Nitrous Acid and Nitrogen Dioxide from Nitrate Photolysis in Acidic Aqueous Solutions

Nitrate (NO3¯) is an abundant component of aerosols, boundary layer surface films, and surface water. Photolysis of NO3¯ leads to NO2 and HONO, both of which play important roles in tropospheric ozone and OH production. Field and laboratory studies suggest that NO3¯ photochemistry is a more importan...

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Bibliographic Details
Published in:Environmental science & technology 2014-10, Vol.48 (20), p.11991-12001
Main Authors: Scharko, Nicole K, Berke, Andrew E, Raff, Jonathan D
Format: Article
Language:English
Subjects:
Aerosols - chemistry
Applied sciences
Aqueous solutions
Atmospheric pollution
Boundary layer
Exact sciences and technology
Nitrates
Nitrates - chemistry
Nitrogen dioxide
Nitrogen Dioxide - chemistry
Nitrogen Oxides - chemistry
Nitrous Acid - chemistry
Photochemistry
Photochemistry - methods
Photodegradation
Photolysis
Pollutants physicochemistry study: properties, effects, reactions, transport and distribution
Pollution
Solutions - chemistry
Water - chemistry
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Summary:Nitrate (NO3¯) is an abundant component of aerosols, boundary layer surface films, and surface water. Photolysis of NO3¯ leads to NO2 and HONO, both of which play important roles in tropospheric ozone and OH production. Field and laboratory studies suggest that NO3¯ photochemistry is a more important source of HONO than once thought, although a mechanistic understanding of the variables controlling this process is lacking. We present results of cavity-enhanced absorption spectroscopy measurements of NO2 and HONO emitted during photodegradation of aqueous NO3¯ under acidic conditions. Nitrous acid is formed in higher quantities at pH 2–4 than expected based on consideration of primary photochemical channels alone. Both experimental and modeled results indicate that the additional HONO is not due to enhanced NO3¯ absorption cross sections or effective quantum yields, but rather to secondary reactions of NO2 in solution. We find that NO2 is more efficiently hydrolyzed in solution when it is generated in situ during NO3¯ photolysis than for the heterogeneous system where mass transfer of gaseous NO2 into bulk solution is prohibitively slow. The presence of nonchromophoric OH scavengers that are naturally present in the environment increases HONO production 4-fold, and therefore play an important role in enhancing daytime HONO formation from NO3¯ photochemistry.
ISSN:0013-936X
1520-5851
DOI:10.1021/es503088x