Atmospheric Photochemistry in Low-and High-NOx Regimes

Abstract

Atmospheric photochemistry of <TEX>$O_3-NOx-RH$</TEX> were considered theoretically, to clarify the reasons for the different trends of between the formation of photochemical oxidants (Ox) and its primary pollutants for the Low-and High-NOx regimes. Equations of OH, <TEX>$HO_2$</TEX>, and production of ozone (<TEX>$O_3$</TEX>) as a function of nitrogen oxides (NOx) and reactive hydrocarbons (RH) were represented in this study. For the Low-NOx regime, <TEX>$HO_2$</TEX> radical is proportional to RH but independent of NOx. OH radical is proportional to NOx but inversely-proportional to RH. <TEX>$O_3$</TEX> production is proportional to NOx but has a weak dependence on RH. For the High-NOx regime, OH and <TEX>$HO_2$</TEX> radicals concentrations and <TEX>$O_3$</TEX> production are proportional to RH but inversely-proportional to NOx. In addition, the Osaka Bay and surrounding areas of Japan were evaluated with the mass balance of odd-hydrogen radicals (Odd-H) using CBM-IV photochemical mechanism, in order to distinguish the Low- and High-NOx regimes. The Harima area (emission ratio, RH/NOx = 6.1) was classified to the Low-NOx regime. The Hanshin area (RH/NOx = 3.5) and Osaka area (RH/NOx = 4.3) were classified to the High-NOx regime.