Trace substances in rain water: concentration variations during convective rains, and their interpretation

Abstract

The temporal changes of contaminant concentrations in rain water samples collected sequentially at a fixed point are dependent upon both the rain scavenging and drop growth processes and the advective effects of the motion field upon the scalar field of concentration variations in the rain cloud. The observations that rainfall intensity and contaminant concentrations are usually negatively correlated, but occasionally for short periods are positively correlated, are explained. Periods of positive correlation appear mainly because of a predominating advective effect, whereas, all drop growth and scavenging processes operate to produce the negative correlation. In the massive storms characterized by Browning (1964) as “SR‐storms” and by Newton (1966) as “persistent”, an extraordinarily well‐organized downdraft is inferred. The strong evaporative effect of this downdraft upon rain in contact with it produces an atypical variation of concentrations in relation to rainfall rates. An example of this is presented.

Relations Between Bulk Precipitation, PM10 Composition and Meteorological Conditions in the Metropolitan Area of Costa Rica

“…Table 12 shows the Spearman correlations between some ionic species in PM 10 and bulk precipitation. There was a negative correlation of pH value with PM 10 . As pollution aerosols, such as SO 4 2-and NO 3 -that mostly exist in finer particles are the major contributors to acidity while they are scavenged into rainwaters [21,22].…”

“…Moreover, rainfall volume is a key parameter for rain composition as it determines the degree of washout of the atmosphere, influencing therefore the global concentration of rain. Relationships between ion concentration and rainfall rate have also been reported [10]. Finally, the duration of the rain-free period, preceeding a rain event, influence the concentration of suspended particles and gases at rain beginning.…”

“…For PM 10 samples from each filter, a strip of 2.54 cm wide and 23.0 cm in length was cut. Then, it was placed in a 150 ml Beaker, 75 ml of deionized water (DW) was added.…”

“…For all the sampling sites, the predominants ions were SO 4 2-and Na + followed by Cl -, PO 4 3-, NH 4 + y NO 3 -for those with high vehicular flow (CAT-SJ, CCLR-BE, REC-HE) while for sites in transition from commercial to residential area, the concentration of PO 4 3-turned out to be greater than that of Cl -. Ionic constituents represent 22.0, 20.0, 14.6, 20.8 and 15.7% of total mass of PM 10 , collected in the sampling sites of CAT-SJ, JE-SJ, REC-HE, GOB-HE and CCLR-BE respectively. In the case of heavy metals, Fe, Al, Mn and Cu concentrations were greater in PM 10 while Cr and Ni were the less abundant species, with the exception of the sampling sites located in Heredia city, where Cr showed higher levels to those found in other places.…”

“…Ionic constituents represent 22.0, 20.0, 14.6, 20.8 and 15.7% of total mass of PM 10 , collected in the sampling sites of CAT-SJ, JE-SJ, REC-HE, GOB-HE and CCLR-BE respectively. In the case of heavy metals, Fe, Al, Mn and Cu concentrations were greater in PM 10 while Cr and Ni were the less abundant species, with the exception of the sampling sites located in Heredia city, where Cr showed higher levels to those found in other places. Values in bold are significant at a p < 0.05, n= 38.…”