Abstract
Abstract. As an important atmosphere constituent, sulfate aerosols exert profound impacts on climate, the ecological environment, and human health. The Tibetan Plateau (TP), identified as the “Third Pole”, contains the largest land ice masses outside the poles and has attracted widespread attention for its environment and climatic change. However, the mechanisms of sulfate formation in this specific region still remain poorly characterized. An oxygen-17 anomaly (Δ17O) has been used as a probe to constrain the relative importance of different pathways leading to sulfate formation. Here, we report the Δ17O values in atmospheric sulfate collected at a remote site in the Mt. Everest region to decipher the possible formation mechanisms of sulfate in such a pristine environment. Throughout the sampling campaign (April–September 2018), the Δ17O in non-dust sulfate show an average of 1.7 ‰±0.5 ‰, which is higher than most existing data on modern atmospheric sulfate. The seasonality of Δ17O in non-dust sulfate exhibits high values in the pre-monsoon and low values in the monsoon, opposite to the seasonality in Δ17O for both sulfate and nitrate (i.e., minima in the warm season and maxima in the cold season) observed from diverse geographic sites. This high Δ17O in non-dust sulfate found in this region clearly indicates the important role of the S(IV)+O3 pathway in atmospheric sulfate formation promoted by conditions of high cloud water pH. Overall, our study provides an observational constraint on atmospheric acidity in altering sulfate formation pathways, particularly in dust-rich environments, and such identification of key processes provides an important basis for a better understanding of the sulfur cycle in the TP.
Highlights
As a predominant chemical component of atmospheric aerosols, sulfate (SO24−) plays an important climatic role as it tend to make clouds more reflective and increases their lifetimes, thereby causing a net cooling effect on the planetPublished by Copernicus Publications on behalf of the European Geosciences Union.K
Sulfate is mainly produced within the atmosphere by the oxidation of sulfur dioxide (SO2), which is largely emitted from combustion processes and volcanoes and is generated by oxidation of other sulfur-containing species such as dimethyl sulfide (DMS) emitted by oceanic phytoplankton
4 times higher than those during the monsoon season. It is likely the seasonal variations in the main ionic concentrations mainly result from the scavenging effect of precipitation in the monsoon season and more frequent dust storms in the pre-monsoon season (Kang et al, 2000)
Summary
K. Wang et al.: Isotopic constraints on atmospheric sulfate formation pathways (Charlson et al, 1992; Kulmala et al, 2000). Wang et al.: Isotopic constraints on atmospheric sulfate formation pathways (Charlson et al, 1992; Kulmala et al, 2000) It is a major source of acidity in aerosols and cloud water and is implicated in acid deposition that exerts adverse effects on the ecological environment and human health (Chang et al, 1987). SO2 is mainly oxidized by hydroxyl radical (OH) to produce sulfuric acid (H2SO4) that can nucleate new particles and increase aerosol number density and the population of cloud condensation nuclei (Kulmala et al, 2000).
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