Emissions of atmospherically important nitrous acid (HONO) gas from northern grassland soil increases in the presence of nitrite (NO2-)

Several studies have shown that the use of nitrogen fertilizers increases the emission of nitric oxide (NO) and nitrous oxide (N2O) from agricultural soils. Nitrous acid (HONO) is another form of gaseous N which increase the reactivity potential in the atmosphere by forming OH radicals in photolysis and further oxidize pollutants e.g. methane. It has recently been discovered that soil is a source of HONO. In our experiment with grassland (Phleum pratense L.), we found that HONO emissions increased up to 14 mu g N m(-2) h(-1) in the plot receiving annually 450 kg N ha(-1) and were strongly linked with soil nitrite (NO2-) concentration and pH. A strong correlation between HONO and NO emissions was also observed. This finding suggests that agricultural soils could be an important source of HONO and its emission is primarily dependent soil NO2- concentration. Moreover, in agricultural soils the production pathway of HONO and NO could be similar and more studies on the effect of fertilization on HONO emission are needed.