Photochemical emissions of HONO, NO2 and NO from the soil surface under simulated sunlight

Abstract

Emissions of HONO, NO 2 and NO from different soils under simulated sunlight were investigated using a flow reactor at ambient pressure. Enhanced emissions of HONO, NO 2 and NO were observed when soils were exposed to the simulated sunlight. NO 3 − and NO 2 − partly contributed to the HONO and NO formations, whereas NH 4 + and NH 2 OH played minor roles in HONO, NO 2 and NO emissions from the soil. The emission flux densities of HONO ( F HONO ), NO 2 ( F N O 2 ) and NO ( F NO ) significantly depended on environmental conditions, including irradiation intensity, relative humidity (RH), temperature and pH. F HONO , F N O 2 and F NO linearly increased with increasing irradiation intensity in the range of 0–320 W/m 2 . Maximum values of F HONO , F N O 2 and F NO appeared at RH = 55%. F HONO and F NO increased while F N O 2 decreased with increasing the temperature in the range of 278–338 K. Maximum F HONO and F N O 2 values appeared at pH = 8 while larger F NO values occurred at pH of 2 and 8. Atmospheric implications about the photochemical emission of HONO from soil contributing to HONO in the atmosphere were also discussed. • Light significantly enhanced HONO, NO 2 and NO emissions from soils. • NO 3 − and NO 2 − partly contributed to the HONO and NO emissions from the soil. • HONO, NO 2 and NO emission flux densities depended on the environmental conditions.