Temporal and spatial variability of atmospheric ammonia in the Lombardyregion (Northern Italy)

Özet

This work investigates the spatial and temporal variability of atmospheric ammonia concentrations in theLombardy region in Northern Italy, where its continuous measurement at hourly resolution began in 2007 atmonitoring sites representative of three different land use areas (urban, rural, and mountain locations).Ammonia concentration data have been jointly analyzed with wind direction and speed to highlight the asso-ciation between the origin of the air masses and the concentration levels observed at the monitoring sites farfrom the primary sources, essentially consisting of farming activities and cattle and pigs breeding located in thesoutheastern part of the Lombardy region. The annual average concentrations of ammonia observed at urban(4.4–13.4μgm−3range) and rural (17–35μgm−3range) monitoring sites are in substantial agreement withliterature data, which are however limited and strongly influenced by the measurement techniques used. Thelowest concentration levels (1.1–5.8μgm−3range) are observed at the monitoring sites in the mountain areas.Both the seasonal and daily time patterns of the concentrations appear strongly related to some features of themeasurement sites, namely with regard to their exposure to agricultural activities, whose seasonal practices arisein emissions responsible for strong variations in the ammonia atmospheric levels. Conversely, in the mountainareas in the north of region, local conditions affecting the atmospheric circulation seem to play a more importantrole than local sources, with the highest concentrations occurring when the breezes transport NH3-rich airmasses from the southern part of the region.