Quantitative reduction of particulate nitrate to nitric oxide by a molybdenum catalyst: Implications for NOy measurements in the marine boundary layer

NaNO3 is one of the most important species in total odd nitrogen oxides (NOy), especially with respect to nitrogen supply to the ocean as a nutrient. The reduction efficiencies (RE) of NaNO3 by a molybdenum catalyst were measured in order to investigate the contribution of nitrates to the measurement of NOy. NaNO3 particles with 3-mu m diameter were reduced to NO quantitatively by a molybdenum catalyst. However, RE decreased with particle diameter to 49.3 +/- 9.1% (1 sigma) for NaNO3 particles with 9-mu m diameter. Meanwhile, quantitative reduction was observed for NaNO3/NaCl particles regardless of particle diameter. RE was 92.6 +/- 2.8% (1 sigma) for NaNO3/NaCl particles even as large as 12-mu m diameter. The decrease of RE with particle diameter for NaNO3 is caused by the nitrate concentrations rather than particle diameter. We concluded that aerosols containing NaNO3 can be converted quantitatively by a molybdenum catalyst in the atmosphere. The confirmation of such quantitative reduction is the first-time.