Assessing the seasonal dynamics of nitrate and sulfate aerosols at the South Pole utilizing stable isotopes
Atmospheric nitrate (NO 3 − = particulate NO 3 − + gas‐phase nitric acid [HNO 3 ]) and sulfate (SO 4 2− ) are key molecules that play important roles in numerous atmospheric processes. Here, the seasonal cycles of NO 3 − and total suspended particulate sulfate (SO 4 2− (TSP) ) were evaluated at the South Pole from aerosol samples collected weekly for approximately 10 months (26 January to 25 October) in 2002 and analyzed for their concentration and isotopic compositions. Aerosol NO 3 − was largely affected by snowpack emissions in which [NO 3 − ] and δ 15 N(NO 3 − ) were highest (49.3 ± 21.4 ng/m 3 , n = 8) and lowest (−47.0 ± 11.7‰, n = 5), respectively, during periods of sunlight in the interior of Antarctica. The seasonal cycle of Δ 17 O(NO 3 − ) reflected tropospheric chemistry year‐round with lower values observed during sunlight periods and higher values observed during dark periods, reflecting shifts from HO x ‐ to O 3 ‐dominated oxidation chemistry. SO 4 2− (TSP) concentrations were highest during austral summer and fall (86.7 ± 73.7 ng/m 3 , n = 18) and are indicated to be derived from dimethyl sulfide (DMS) emissions, as δ 34 S(SO 4 2− ) (TSP) values (18.5 ± 1.0‰, n = 10) were similar to literature δ 34 S(DMS) values. The seasonal cycle of Δ 17 O(SO 4 2− ) (TSP) exhibited minima during austral summer (0.9 ± 0.1‰, n = 5) and maxima during austral fall (1.3 ± 0.3‰, n = 6) and austral spring (1.6 ± 0.1‰, n = 5), indicating a shift from HO x ‐ to O 3 ‐dominated chemistry in the atmospheric derived SO 4 2− component. Overall, the budgets of NO 3 − and SO 4 2− (TSP) at the South Pole were complex functions of transport, localized chemistry, biological activity, and meteorological conditions, and these results will be important for interpretations of oxyanions in ice core records in the interior of Antarctica.