MEASUREMENT OF NITROUS-ACID IN MILAN, ITALY, BY DOAS AND DIFFUSION DENUDERS

Measurements of the atmospheric mixing ratio of nitrous acid have been carried out by means of the differential optical absorption system (D OAS) during a wintertime field study carried out in the urban area of Milan (Italy). Preliminary laboratory calibration of the DOAS was carr ied out by making use of a standard source of pure HONO which provided an interference-free UV absorption spectrum of HONO and recalculation of the absorption cross-section of this compound. Very high HONO mixi ng ratios, up to values exceeding 10 ppb, were measured during the cam paign. DOAS results were compared with those obtained by using the ann ular denuder technique and good agreement was observed during the whol e measurement period. On the basis of these measurements, a study on t he relationship between the dynamic conditions of the lower boundary l ayer and the temporal trend of HONO mixing ratio can be carried out, i n order to obtain indications about the sources of this species in urb an atmospheres. Copyright (C) 1996 Elsevier Science Ltd