Chemical composition, sources, and deposition fluxes of water-soluble inorganic ions obtained from precipitation chemistry measurements collected at an urban site in northwest China

Abstract

Precipitation samples were collected at an urban site in Xi'an, northwest China during March to November in 2009 and were then analyzed to determine the pH and concentrations of water-soluble inorganic ions (Na(+), NH(4)(+), K(+), Mg(2+), Ca(2+), SO(4)(2-), NO(3)(-), Cl(-), and F(-)) in precipitation. The pH of precipitation ranged from 4.1 to 7.6 for all of the samples with an annual volume-weighted mean of 6.4. While a large portion of the precipitation events were weakly acidic or alkaline, around 30% of the precipitation events in the autumn were strongly acidic. Precipitation events with air masses from the northeast and the southeast were weakly acidic while those with air masses from the northwest and the southwest were alkaline. SO(4)(2-), Ca(2+), NH(4)(+), and NO(3)(-) were dominant ions in the precipitation, accounting for 37%, 25%, 18%, and 9%, respectively, of the total analyzed ions. Ca(2+) and NH(4)(+) were found to be the major neutralizers of precipitation acidity; however, the contribution of Mg(2+), although much lower than those of Ca(2+) and NH(4)(+), was important, in many cases, in changing the precipitation from weakly acidic to weakly alkaline. Enrichment factor analysis confirmed that SO(4)(2-) and NO(3)(-) were produced from anthropogenic sources, Ca(2+), K(+), and 80% Mg(2+) were from crustal sources, and Na(+), Cl(-), and ∼20% of Mg(2+) were from marine sources. The annual wet depositions were estimated to be 3.5 t km(-2) per year for sulfur; 2.3 t km(-2) per year for nitrogen, of which 0.8 t km(-2) per year was oxidized nitrogen and 1.5 t km(-2) per year was reduced nitrogen; and 3.0 t km(-2) per year for Ca(2+).

Chemical and sulfur isotopic composition of precipitation in Beijing, China

“…3); hence, the fraction of acidic precipitation was also higher in autumn and summer compared to winter and spring. This is comparable to the results from other regions in North China (Shen et al 2012;Zhang et al 2012) but reverse to data from Hangzhou (Xu et al 2011) and Anhui (Huang et al 2012) in the south of China. The acidity of the precipitation depends on the concentrations of acid-forming ions and of alkaline species neutralizing the acidity ).…”

Characteristics of atmospheric mercury deposition and size-fractionated particulate mercury in urban Nanjing, China

“…Formate is indicative of volatile organic compounds mostly emitted from vegetation (Dordevic et al, 2010). Good correlations were seen between calcium and potassium (r = 0.76), as well as calcium and magnesium (r = 0.92), which suggested their crustal origin, namely local resuspended soil and dust from inland cities (Guentzel et al, 1998;Shen et al, 2012;Salve et al, 2006). In view of good correlations of mercury with formate, calcium, potassium, and magnesium (r = 0.73), natural sources including vegetation and resuspended soil should be considered as an important factor influencing the wet deposition of mercury in Nanjing.…”

Day-Night Differences, Seasonal Variations and Source Apportionment of PM10-Bound PAHs over Xi’an, Northwest China

“…Whereas in summer conditions with high temperature, strong solar radiation and high O 3 level, PAHs favor to partition in the gas phase or convert to their oxidative derivatives via heterogeneous reactions with gas-phase oxidants [5,40]. The frequent rainfall in summer is also an important factor reducing the particulate PAHs levels through wet scavenging process [41].…”