Southern Hemisphere mid- and high-latitudinal AOD, CO, NO2, and HCHO: spatiotemporal patterns revealed by satellite observations

Dha Hyun Ahn,Jhoon Kim,Sang Seo Park,Ja-Ho Koo,Seong-Joong Kim,Yun Gon Lee,Taejin Choi

doi:10.1186/s40645-019-0277-y

Abstract

To assess air pollution emitted in Southern Hemisphere mid-latitudes and transported to Antarctica, we investigate the climatological mean and temporal trends in aerosol optical depth (AOD), carbon monoxide (CO), nitrogen dioxide (NO2), and formaldehyde (HCHO) columns using satellite observations. Generally, all these measurements exhibit sharp peaks over and near the three nearby inhabited continents: South America, Africa, and Australia. This pattern indicates the large emission effect of anthropogenic activities and biomass burning processes. High AOD is also found over the Southern Atlantic Ocean, probably because of the sea salt production driven by strong winds. Since the pristine Antarctic atmosphere can be polluted by transport of air pollutants from the mid-latitudes, we analyze the 10-day back trajectories that arrive at Antarctic ground stations in consideration of the spatial distribution of mid-latitudinal AOD, CO, NO2, and HCHO. We find that the influence of mid-latitudinal emission differs across Antarctic regions: western Antarctic regions show relatively more back trajectories from the mid-latitudes, while the eastern Antarctic regions do not show large intrusions of mid-latitudinal air masses. Finally, we estimate the long-term trends in AOD, CO, NO2, and HCHO during the past decade (2005–2016). While CO shows a significant negative trend, the others show overall positive trends. Seasonal and regional differences in trends are also discussed.

Highlights

Antarctica is known as an isolated region due to its geographical distance from human activity, as well as the surrounding polar vortex hindering meridional exchange
In Africa, the aerosol optical depth (AOD) maximum occurs in September, consistent with the season of peak biomass burning in Africa (Das et al 2017)
The monthly distribution in South America has the same pattern as in Africa, indicating the likely contribution of biomass burning to the level of AOD

Summary

Introduction

Antarctica is known as an isolated region due to its geographical distance from human activity, as well as the surrounding polar vortex hindering meridional exchange. If we focus on the median pattern, which is free from outlier influence, analysis of long-term satellite observations can assist in the investigation of climatological patterns and temporal trends. Through this analysis, we expect to diagnose whether changes in the mid-latitudinal atmospheric composition in the Southern Hemisphere tend to increase Antarctic air pollution. Mean values are generated based solely on data having reliable QAC values, meaning that our analysis is free from the cloud effect This product can be used in this study without additional screening tasks. Climatological mean Based on the analysis of satellite data in the mid-latitudes with interpretation of back trajectory patterns, we can diagnose the impact of meridional transport to the Antarctic atmosphere. The trend is considered significant at the 95% confidence level when the p value is less than 0.05

Results and discussion

Conclusions

Availability of data and materials Not applicable