A More Important Role for the Ozone‐S(IV) Oxidation Pathway Due to Decreasing Acidity in Clouds

Abstract

Clouds significantly affect the Earth's radiation budget and play a critical role in atmospheric sulfate formation. The pathways of S(IV) oxidations have recently caused a controversial attention under severe haze episodes due to the variable acidity and water content in aerosol particles. In this study, a total of 158 cloud samples were collected from 2014 to 2018 at the summit of Mt. Tai, China, to explore the roles of atmospheric oxidants in aqueous S(IV) oxidation. The results showed that the averaged pH value of cloud water increased dramatically from 3.

Atmospheric Hydrogen Peroxide (H2O2) at the Foot and Summit of Mt. Tai: Variations, Sources and Sinks, and Implications for Ozone Formation Chemistry

“…A recent study reported an increasing trend of H 2 O 2 concentrations in the cloud samples at the summit of Mt. Tai from 2014 to 2018 (Li et al, 2020)…”

Acidity and the multiphase chemistry of atmospheric aqueous particles and clouds

“…As a consequence, the increased aqueous-phase partitioning enables higher chemical processing rates of weak acids such as SO2, HONO and organic carboxylic acids. Both lower acidity and stronger buffering can support faster S(IV) to S(VI) conversions due to the higher efficiency of other chemical pathways such as ozone oxidation (Li et al, 2020b) and therefore reduce the tropospheric lifetime (and incloud lifetime) of SO2. Therefore, under future conditions with a lower overall SO2 budget, the increased secondary sulfate mass formation probabilities may compensate at least partly the reduced sulfate formation potential.…”

Evaluation of SO<sub>2</sub>, SO<sub>4</sub><sup>2−</sup> and an updated SO<sub>2</sub> dry deposition parameterization in UKESM1

“…Total column SO 2 (TCSO 2 ) measurements came from the Ozone Monitoring Instrument (OMI), which were obtained from the Goddard Earth Sciences Data and Information Services Centre (https://aura.gesdisc.eosdis.nasa.gov/data/Aura_OMI_Level2/ OMSO2.003) (Li et al, 2020). OMI is situated on-board NASA's polar-orbiting Aura satellite launched in 2004 with a local overpass time of approximately 13:45.…”

“…Of these, the satellite data sets with the best temporal resolution and spatial coverage for SO 2 are from the Ozone Monitoring Instrument aboard the NASA Earth Observing System Aura spacecraft (Fioletov et al, 2016). Although biases in the SO 2 retrieval from OMI limit its use at high and low latitudes in winter and over ares with low atmospheric loading, they do provide valuable information over regions where there are no long term, or even any ground-based observations (Li et al, 2020;Levelt et al, 2018). This paper is configured as follows; the model (UKESM1), the model simulations, observation data sets and modifications to UKESM1's SO 2 dry deposition parameterization are described in Section 2.…”

“…The model bias is also larger in DJF compared with JJA, but the SO 2 concentrations are over-predicted to such a large degree in this region that it is difficult to determine if there is any seasonality in this bias. .81 µg m −3 and 2.85 µg m −3 in DJF and JJA respectively.3.5 Evaluation of total column SO 2 in UKESM1 against satellite observations Statistics between model runs and OMI TCSO2 monthly zonally averaged (median) time series(2005)(2006)(2007)(2008)(2009)(2010)(2011)(2012)(2013)(2014) for three latitude bands SO 2 (TCSO 2 ) from UKESM1 and OMI, and the difference between them for DJF and JJA.Note that the quality control for solar zenith angle results in no data availability above 65 • N degrees or below 65 • S in the winter months and due to OMI's weaker sensitivity to retrieving SO 2 in remote regions we focus on comparing TCSO 2 over source and outflow regions(Li et al, 2020). Figures8 a-dshow that UKESM1 and OMI broadly agree on the location of the main northern hemisphere (NH) source regions including China, India, Europe and the USA.…”