Abstract
Measurements of surface fluxes of HONG (and for comparison HN0
3) made above grassland in eastern England by the gradient technique are reported. The HONO data divide equally between periods with net upward and net downward fluxes. The occurrence of upward fluxes is associated with NO
2 concentrations in excess of
ca. 10 ppb and the data are interpreted in terms of the net effect of two processes. On the one hand, HONG is dry deposited with considerable efficiency (deposition velocities 0.2–1.7 cm s
−1) whilst on the other, HONG is formed at the surface by heterogeneous reactions of NO
2. At low NO
2 concentrations the deposition process dominates, whilst with high N0
2 there is a net release of HONO to the atmosphere. The magnitudes of upward fluxes of HONG are consistent with production rates of HONO measured in the atmosphere in this and other studies, and it appears that heterogeneous production at the surface might account for the hitherto unidentified major source of atmospheric HONO.