Concentrations of nitrous acid, nitric acid, nitrite and nitrate in the gas and aerosol phase at a site in the emission zone during ESCOMPTE 2001 experiment

Ground-based measurements were performed at the “Expérience sur Site pour COntraindre les Modèles de Pollution atmosphérique et de Transport d`Emissions” (ESCOMPTE) field site E3 (Realtor) about 30 km north of the urban environment of Marseille and east of the industrial centre Berre pond to investigate the formation of nitrous and nitric acid and to detect the distribution of reactive N-species between the gas and particle phase during photochemical pollution events. A wet denuder sampling for gases followed by a steam jet collection for aerosols was both coupled to anion chromatographic analysis. The analytical system provided data continuously with 30-min time resolution between June 13 and July 13, 2001. Indications for heterogeneous formation of nitrous acid during nighttime and daytime on ground and aerosol surfaces were found, the average HNO2/NO2 ratio was 6%. Highest concentrations were observed during two episodes of strong pollution accumulation when sea breeze transported industrial, traffic and urban pollution land-inwards. After nocturnal heterogeneous formation (about 0.1 ppbv h−1 were estimated corresponding to increasing HNO2/NO2 ratios) and accumulation processes up to 1.2 ppbv HNO2 were observed. Their photolysis produces up to 5-9×106 OH cm−3 s−1 and will contribute significantly to initiation of the daily photochemistry in the lowest part of the troposphere. For the key tropospheric species, HNO3 daily peaks up to 4 ppbv were detected.