Five-year record of atmospheric precipitation chemistry in urban Beijing, China

Abstract

Abstract. To investigate the chemical characteristics of precipitation in the polluted urban atmosphere in Beijing and possible mechanisms influencing their variations, a total of 131 event-based precipitation samples were collected from March 2001 to August 2005. The concentrations of major ions in the samples were analyzed by using ion chromatography. Intermediate pH (6.1-7.3) was recorded in approximately two-thirds of the precipitation samples and acidic pH (4.2-5.6) in only 16 % of the samples. However, the precipitation acidity was on the growth track and the process was likely being accelerated. SO 2− 4 , NO − 3 , NH + 4 , and Ca 2+ were the most abundant ions in the precipitations, with their single volume-weighted mean (VWM) concentration all above 100 µeq l −1 . The two major anions and two major cations accounted for more than 80 % of total anionic and cationic mass, respectively. The VWM SO 2− 4 concentration decreased by 13 % compared to that during 1995-1998, much less than the 58 % reduction in the annual average SO 2 concentration from 1998 to 2005 in Beijing. What seems more counterintuitive is that the VWM NO − 3 concentration nearly doubled over the period although the annual average NO 2 concentration decreased by 5 % from 1998 to 2005. These results imply that the conversion of gaseous precursors to acid compounds and/or the regional transport were reinforced over the decade. The average ratio of neutralizing potential to acidifying potential (i.e. NP/AP) was as high as 1.2 but experienced an evident decline trend. This was mainly ascribed to reduced input of NH 4 presented an increasing trend over the study period, suggesting that the contribution of NO − 3 to the precipitation acidity increased in recent years. However, the mean ratio was only 0.37 ± 0.11 in the study period, which is significantly lower than those reported in some metropolitan areas in developed countries. This shows that the precipitation acidity in Beijing was still dominantly from SO 2 while the SO 2 contribution was progressively substituted by NO x .

Source Identification of Acid Rain Arising over Northeast China: Observed Evidence and Model Simulation

“…The increasing long heating period in winter, potential source of abundant sulfur emissions, might not be significantly balanced by NO x emissions essentially from regional mobile traffic. Over Dalian, the yearly ratio was 2.35 with high concentrations of both nssSO 4 2-and NO 3 -in winter, which is similar with that in Beijing with the value of 2.7 based on the five-year measurements reported by Yang et al (2012). This reflects the strong impact of local NO x emissions over Dalian where the mobile traffic is actually much more intense than that in Dandong.…”

“…In comparison with Dandong, the acid rain was obviously less pronounced in Dalian city with relatively higher yearly pH vwa at HJS, LS (4.5) and GJZ (5.15). However, the acid rain in both cities seemed to be at the similar levels as those observed in Southwestern China (pH are in the range of 4.1-4.6) and Yangzi River (pH vwa 4.5) by (Aas et al, 2007) and (Huang et al, 2008), and more critical than the acidification process observed in Beijing (5 years rainfall records with pH vwa = 6.2) reported by Yang et al (2012).…”

“…S2(a)), revealing anion deficiency in the city, in agreement with previous literatures. This might due to some unmeasured anions such as short chain organic acids (Hontoria et al, 2003;Yang et al, 2012). Overall, the ion and conductivity balance in both Dalian and Dandong cities seemed to be reliable according to the acceptable range by US EPA (Table S1), although the organic anions were absent.…”

Spatial distribution and temporal variations of atmospheric sulfur deposition in Northern China: insights into the potential acidification risks

“…Under the current national monitoring networks, only general urban air quality parameters and rainwater pH are measured, whereas little effort has been invested in determining the chemistry of the pollutants (Tang et al, 2010). Rapid advances have been made in recent years in the investigation of the chemical constituents responsible for the variations in precipitation pH (Huang et al, 2008;Sun et al, 2010;Tsai et al, 2011;Wai et al, 2005;Yang et al, 2012a), but most studies have been limited to a single site/year. Acid deposition can occur via the dry deposition of gases and particles and by wet deposition from rain, snow, clouds and fog (Flechard et al, 2011).…”

Wet Deposition of Trace Metals at a Typical Urban Site in Southwestern China: Fluxes, Sources and Contributions to Aquatic Environments

“…About 10 years ago, atmospheric deposition studies had mainly focused on the acid rain causing ions (NO − 3 and SO 2− 4 ), due to the great harm caused by acid deposition [12,13]. With increasing human health concerns and the improvement of technology for detecting TMs, researchers have begun to pay attention to atmospheric TM deposition.…”