Below-cloud ammonia scavenging in convective thunderstorms at a coastal research site in Tampa, FL, USA

Evolution of the Concentration of Inorganic Ions during the Initial Stages of Precipitation Events

“…Conversely, the most readily scavenged ion is Na + (Tables I and II). The relative ease of scavenging, and hence derived b values, implied by these data are of similar magnitude to those for SO 4 2− and NO 3 − derived by Minoura and Iwasaka (1997) and b for NH 4 + developed from data presented in Mizak et al (2005) (Table II). The data collected by Minoura and Iwasaka (1997) implies a larger absolute difference in b for SO 4 2− and NO 3 − than is manifest in our data and that NO 3 − was 'scavenged The exponential fits are shown in Figure 1 by the solid line, while the power law fits are shown by the dashed line.…”

“…As a result, the scavenging coefficients for all ions are statistically indistinguishable -i.e., the uncertainty bounds defined by the 95% confidence intervals on the b values from each ion overlap. A similar inference can be drawn from analysis of NH 4 + concentrations in five precipitation events in Florida (Mizak et al, 2005) (Table II) and also data presented in a literature summary by Claassen and Halm (1995b). The latter indicates the value of β in Equation (1) for SO 4 2− (in cm −1 ) from various studies range from a low of 3 to a maximum of 22 across seven studies, while β for Cl − from three studies ranged between 14 and 28 (cm −1 ).…”

“…Data from the five events presented in Mizak et al (2005) were also analyzed individually to derive event-specific b values using Equation (2). The results ranged from −0.035 to −0.099.…”

“…While each precipitation event is unique, in general theoretical considerations and previous observations have indicated significant enrichment in the initial stages of precipitation events and in light precipitation events (e.g., Asman, Jonker, Slanina, & Baard, 1982;Burch, Waldner, & Fritschi, 1996;Claassen & Halm, 1995b;Kennedy, Zellweger, & Avanzino, 1979;Khare et al, 1996;Kins, 1982;Lim, Jickells, & Davies, 1991;Mizak et al, 2005;Pryor & Barthelmie, 2005;Radojevic & Lim, 1995;Seto et al, 2002;Seymour & Stout, 1983). Data collected during five precipitation events (all summertime liquid phase events) in the northeastern USA indicate up to 50% of the total sulfate (SO 4 2− ) and nitrate (NO 3 − ) deposition can occur during the first 15%-20% of the total rainfall and that after a precipitation depth of 4.6 mm ion concentrations tend to asymptote to a constant value for the remainder of the event (Seymour & Stout, 1983).…”

δ15N–NH4+ variations of rainwater: Application of the Rayleigh model

“…Ammonium concentrations in particles were reduced only about 34% in rainy days in Guiyang (Xiao and Liu, 2004). The scavenging coefficients of gaseous ammonia and 0.5 μm ammonium particles are between 0.6 and 12 h −1 , and 1 × 10 −4 h −1 in below-cloud scavenging, respectively (Shimshock and Pena, 1988;Seinfeld and Pandis, 1998;Mizak et al, 2005), suggesting that the below-cloud scavenging of ammonium particles can be ignored. More than 88% of ammonium in rainwater comes from belowcloud scavenging of gaseous ammonia in agricultural or industrial areas (Oberholzer et al, 1993;Shen et al, 1993;Mizak et al, 2005).…”