Scavenging of Nitrogen From the Atmosphere by Atmospheric (Rain and Snow) and Occult (Dew and Frost) Precipitation: Comparison of Urban and Nonurban Deposition Profiles

This paper describes the comparison of atmospheric (rain and snow) versus occult (dew and frost) precipitation in terms of scavenging of nitrogen compounds (inorganic and organic) from the atmosphere. Exceptional cases of heavy fog, black ice, hail, and heavy rain were also described. Apart from genesis and morphology of these phenomena, various factors affecting precipitation affinity to scavenging of airborne nitrogen compounds from the atmosphere were investigated. A study simultaneously performed at two sampling points (lowland Central Europe, 30 km away from each other, urban vs. woodland) indicated statistically significant differences in hydrological conditions between areas. Local conditions (urban heat island vs. humid woodland) more likely determined precipitation form, amount, and frequency than the air masses characteristic in the upper troposphere. This (apart from pollution sources) significantly affects the deposition load of nitrogen per area unit. The highest values were obtained with atmospheric precipitation (mainly rainwater) at about 9 and 5 kg N/ha/year in the city and woodland areas, respectively. Nevertheless, the investigated affinity of precipitation to scavenging airborne nitrogen from the atmosphere elicited progressively changing loads of nitrogen per volume unit as follows: dew > rain bulk > snow bulk > rain wet only > frost > snow wet only.