Quantifying the 17O-excess of nitrogen oxides to clarify the reaction processes in urban area

Abstract

The photolysis of nitrous acid (HONO) has been recognized as a potentially important source of OH radicals, which is known as a major oxidant in the atmosphere removing reductive trace gases such as methane and NMHCs. Atmospheric HONO originates from both direct emissions (produced via combustion or biologically produced in soil), and secondary formation (chemically produced from NO₂ or NO in the atmosphere), however, their contributions to the atmospheric HONO production have not been well understood. Here, we determined a ¹⁷O-excess of HONO together with that of its precursors (NO₂ and NO), because ¹⁷O-excess of HONO produced via secondary formation is expected to have highly positive values as those of NO₂ or NO, while no ¹⁷O anomaly should be observed for HONO which is emitted directly from various sources on the ground, making it possible to quantify their contribution to the atmospheric HONO production with ¹⁷O-excess measurement.