04 Dec 2023
 | 04 Dec 2023

Technical Note: A Technique to Convert NO2 to NO2 with S(IV) and its Application to Measuring Nitrate Photolysis

Aaron Lieberman, Julietta Picco, Murat Onder, and Cort Anastasio

Abstract. Nitrate photolysis is a potentially significant mechanism for “renoxifying” the atmosphere, i.e., converting nitrate into nitrogen oxides (nitrogen dioxide (NO2) and nitric oxide (NO)) and nitrous acid (HONO). Nitrate photolysis in the environment occurs through two channels, which produce: (1) NO2 and hydroxyl radical (OH) and (2) nitrite (NO2) and an oxygen atom (O(3P)). Although the aqueous quantum yields and photolysis rate constants of both channels have been established, field observations suggest that nitrate photolysis is enhanced in the environment. Laboratory studies investigating these enhancements typically only measure one of the two photo-channels, since measuring both channels generally requires separate analytical methods and instrumentation. However, measuring only one channel makes it difficult to assess whether secondary chemistry is enhancing one channel at the expense of the other, or if there is an overall enhancement of nitrate photochemistry. Here, we show that the addition of S(IV), i.e., bisulfite and sulfite, can convert NO2 to NO2, allowing measurement of both nitrate photolysis channels with the same equipment. By varying the concentration of S(IV) and exploring method parameters, we determine the experimental conditions that quantitatively convert NO2 and accurately quantify the resulting NO2. We then apply the method to a test case, showing how an OH scavenger in solution prevents the oxidation of NO2 to NO2 but does not enhance the overall photolysis efficiency of nitrate.

Aaron Lieberman, Julietta Picco, Murat Onder, and Cort Anastasio

Status: final response (author comments only)

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse
  • RC1: 'Comment on egusphere-2023-2876', Anonymous Referee #1, 12 Dec 2023
  • RC2: 'Comment on egusphere-2023-2876', Anonymous Referee #2, 07 Jan 2024
  • AC1: 'Comment on egusphere-2023-2876', Cort Anastasio, 20 Feb 2024
Aaron Lieberman, Julietta Picco, Murat Onder, and Cort Anastasio
Aaron Lieberman, Julietta Picco, Murat Onder, and Cort Anastasio


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Short summary
We developed a method that uses S(IV) in aqueous solution to quantitatively convert NO2 to NO2. This allows both species to be quantified using the Griess method. As an example of the utility of the method, we used it to quantify both photolysis channels of nitrate, with and without a scavenger for hydroxyl radical (OH). The results show that without a scavenger, OH reacts with nitrite to form nitrogen dioxide, suppressing the apparent quantum yield of NO2 and enhancing that of NO2.