Anthropogenic imprints on nitrogen and oxygen isotopic composition of precipitation nitrate in a nitrogen-polluted city in southern China

Abstract

Nitric acid (HNO<sub>3</sub>) or nitrate (NO<sub>3</sub><sup>−</sup>) is the dominant sink for reactive nitrogen oxides (NO<sub>x</sub> = NO + NO<sub>2</sub>) in the atmosphere. In many Chinese cities, HNO<sub>3</sub> is becoming a significant contributor to acid deposition. In the present study, we measured nitrogen (N) and oxygen (O) isotopic composition of NO<sub>3</sub><sup>−</sup> in 113 precipitation samples collected from Guangzhou City in southern China over a two-year period (2008 and 2009). We attempted to better understand the spatial and seasonal variability of atmospheric NO<sub>x</sub> sources and the NO<sub>3</sub><sup>−</sup> formation pathways in this N-polluted city in the Pearl River Delta region. The δ<sup>15</sup>N values of NO<sub>3</sub><sup>−</sup> (versus air N<sub>2</sub>) ranged from −4.9 to +10.1‰, and averaged +3.9‰ in 2008 and +3.3‰ in 2009. Positive δ<sup>15</sup>N values were observed throughout the year, indicating the anthropogenic contribution of NO<sub>x</sub> emissions, particularly from coal combustion. Different seasonal patterns of δ<sup>15</sup>N-NO<sub>3</sub><sup>−</sup> were observed between 2008 and 2009, which might reflect different human activities associated with the global financial crisis and the intensive preparations for the 16th Asian Games. Nitrate δ<sup>18</sup>O values (versus Vienna Standard Mean Ocean Water) varied from +33.4 to +86.5‰ (average +65.0‰ and +67.0‰ in 2008 and 2009, respectively), a range being lower than those reported for high latitude and polar areas. Sixteen percent of δ<sup>18</sup>O values was observed lower than the expected minimum of +55‰ at our study site. This was likely caused by the reaction of NO with peroxy radicals; peroxy radicals can compete with O<sub>3</sub> to convert NO to NO<sub>2</sub>, thereby donate O atoms with much lower δ<sup>18</sup>O value than that of O<sub>3</sub> to atmospheric NO<sub>3</sub><sup>−</sup>. Our results highlight that the influence of human activities on atmospheric chemistry can be recorded by the N and O isotopic composition of atmospheric NO<sub>3</sub><sup>−</sup> in a N-polluted city

Three-decade changes in chemical composition of precipitation in Guangzhou city, southern China: has precipitation recovered from acidification following sulphur dioxide emission control?

“…1). This is consistent with back trajectory analysis of NOAA HYSPLIT model, which showed that 62% and 69% of precipitation in 2008 and 2009 were of marine origin, respectively, most of which were transported from the south to Guangzhou city and passed over those former mentioned cities (Fang et al, 2011b).…”

“…Ca 2' is mainly derived from alkaline dust, which has many potential sources, including windblown dust and anthropogenic sources such as industrial and construction activities (Larssen and Carmichael, 2000). High Ca deposition in 2005Á2008 in the study city was most likely caused by intensive construction activities in preparation for the 16th Asian Games (Fang et al, 2011b). We suggest that precipitation may become more acidified in the future because the deposition of alkaline dusts containing Ca is also likely to decrease with stricter SO 2 emission control policy and reduced construction activities.…”

Seasonal dynamics of particulate organic matter and its response to flooding in the Pearl River Estuary, China, revealed by stable isotope (δ13C and δ15N) analyses

“…A sharp decrease in concentrations was observed after the flooding (Figure ), presumably due to the dilution of the ‐rich base‐flow with ‐poor rainwater [ Fang et al ., ], which is consistent with the results reported for other watersheds around the world [e.g., Tesi et al ., ]. The large differences in river discharge were expected to increase nutrient input into the PRE [ Lu et al ., ].…”

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

“…These changes in emissions may increase the extent of N deposition and thereby alter the acid deposition pattern in the future. This argument is partially supported by the fact that the ratio of equivalent concentrations of SO 2− 4 to NO − 3 in precipitation have gradually decreased from 5.4 to 1.7 in Beijing , and from 4.6 to 1.5 in Guangzhou (Fang et al, 2011) over the last three decades. If this trend continues, HNO 3 is expected to play a more important role than H 2 SO 4 in determining the precipitation acidity in the coming decades.…”