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

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 (NO 2 ), 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, NO 2 , 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, NO 2 , and HCHO during the past decade (2005)(2006)(2007)(2008)(2009)(2010)(2011)(2012)(2013)(2014)(2015)(2016). While CO shows a significant negative trend, the others show overall positive trends. Seasonal and regional differences in trends are also discussed.

Formaldehyde total column densities over Mexico City: comparison between multi-axis differential optical absorption spectroscopy and solar-absorption Fourier transform infrared measurements

“…It is worth mentioning that these types of strong spatial heterogeneity scenarios have been observed in different areas of the planet and specific studies of atmospheric constituents have been or are currently being performed in other urbanized and densely populated areas such as North America (Boeke et al, 2011;Chance et al, 2000;Millet et al, 2008); China (Cheng et al, 2015;Zhang et al, 2019), particularly in the Beijing-Tianjin-Hebei region (Zhu et al, 2018); and the Yangtze River Delta area (Chan et al, 2019;Hong et al, 2018;Tian et al, 2018;Wang et al, 2016); and southern Asia (Rana et al, 2019), more specifically India (Chutia et al, 2019;Surl et al, 2018) and Pakistan (Khan et al, 2018;Khokhar et al, 2015). In addition specific case studies have been conducted globally (Wittrock et al, 2006) or in the Southern Hemisphere (Ahn et al, 2019), the Atlantic Ocean (Behrens et al, 2019) and the East China Sea (Tan et al, 2018). Findings of these studies imply the enhanced abundance of HCHO over highly populated areas, areas with increased industrial activity, zones exhibiting biogenic emissions and biomass burning activities and along major highways, and in some instances these identify cases of regional transport of pollutants.…”

“…A MAX-DOAS instrument, designed and built by the Spectroscopy and Remote Sensing Group at CCA-UNAM, was used to conduct sky measurements in the UV-Vis (ultraviolet-visible) region of the electromagnetic spectrum. The MAX-DOAS instrument, which has been collecting data since 2013, is installed on the roof of CCA-UNAM (same location as the FTIR-Vertex instrument) and forms part of a small network (Arellano et al, 2016) of MAX-DOAS instruments that covers part of the MCMA.…”

“…The MAX-DOAS has a theoretical field of view of 0.31 • (Arellano et al, 2016) and performs measurement sequences with a telescope's azimuth angle of 85 • with respect to the north. Each elevation scan of the MAX-DOAS measurements starts with a zenith measurement.…”

“…The dark spectrum is subtracted from all other spectra measured during the sequence (including the zenith spectrum). A detailed instrument description and measurement strategy can be found in Arellano et al (2016) and Friedrich et al (2019). Before conducting retrievals, spectra are filtered with the objective to remove all spectra either with light conditions that are too low (10 % or less of the maximum possible intensity level) or saturated spectra in the retrieval region.…”

Formaldehyde total column densities over Mexico City: comparison between MAX-DOAS and solar absorption FTIR measurements

“…It is worth mentioning that these type of strong spatial heterogeneity scenarios have been observed in different areas of the planet and specific studies of atmospheric constituents have been or are currently being performed in other urbanized and densely populated areas such as North America (Boeke et al, 2011;Chance et al, 2000;Millet et al, 2008), China (Cheng et al, 2015;Zhang et al, 2019), particularly in the Beijing-Tianjin-Hebei region (Zhu et al, 2018) and the Yangtze River Delta area (Chan et al, 2019;Hong et al, 2018;Tian et al, 2018;Wang et al, 2016); South Asia (Rana et al, 2019) and more specifically India (Chutia et al, 2019;Surl et al, 2018) and Pakistan (Khan et al, 2018;Khokhar et al, 2015). In addition specific case studies have been conducted globally (Wittrock et al, 2006) or in the Southern Hemisphere (Ahn et al, 2019), the Atlantic Ocean (Behrens et al, 2019) and the East China Sea (Tan et al, 2018). Findings of these studies imply enhanced abundance of HCHO over highly populated areas, areas with increased industrial activity, zones exhibiting biogenic emissions and biomass burning activities, along major highways and in some instances identifying cases of regional transport of pollutants.…”