, while oxidised N concentrations in the gas phase (from trapping NO 2 and HNO 3 ) were smaller, at 2.6 ± 2.2 nmol N m -3 , and gas-phase WSON concentrations were 18 ± 11 nmol N m -3 . The estimated collection efficiency of the nebulizing samplers for the gas-phase was 88 (±8) % for NH 3 , 37 (±16) % for NO 2 and 57 (±7) % for WSON; reported average concentrations have not been corrected for sampling efficiency. Concentrations in the particle phase were smaller, except for nitrate, at 21 ± 9, 10 ± 6 and 8 ± 9 nmol N m -3 , respectively. The absence of correlation in either phase between WSON and either (NH 3 +NH 4 + ) or NO 3 -concentrations suggests atmospheric WSON has diverse sources. During wet days, concentrations of gas and particle-phase inorganic N were lower than on dry days, whereas the converse was true for WSON. These data represent the first reports of simultaneous measurements of gas and particle phase water-soluble nitrogen compounds in rural air on a daily basis, and show that WSON occurs in both phases, contributing 20-25% of the total watersoluble nitrogen in air, in good agreement with earlier data on the contribution of WSON to total dissolved N in rainfall in the UK.

Water soluble organic nitrogen (WSON) compounds are ubiquitous in precipitation and in the planetary boundary layer, and therefore are a potential source of bioavailable reactive nitrogen. This paper examines weekly rain data over a period of 22 months from June 2005 to March 2007 collected in 2 types of rain collector (bulk deposition and "dry+wet" deposition) located in a semi-rural area 15 km southwest of Edinburgh, UK (N 55°51′44″, W 3°12′19″). Bulk deposition collectors are denoted in this paper as "standard rain gauges", and they are the design used in the UK national network for monitoring precipitation composition. "Dry+wet" deposition collectors are flushing rain gauges and they are equipped with a rain detector (conductivity array), a spray nozzle, a 2-way valve and two independent bottles to collect funnel washings (dry deposition) and true wet deposition. On average, for the 27 weekly samples with 3 valid replicates for the 2 types of collectors, dissolved organic nitrogen (DON) represented 23% of the total dissolved nitrogen (TDN) in bulk deposition. Dry deposition of particles and gas on the funnel surface, rather than rain, contributed over half of all N-containing species (inorganic and organic). Some discrepancies were found between bulk rain gauges and flushing rain gauges, for deposition of both TDN and DON, suggesting biological conversion and loss of inorganic N in the flushing samplers.