Investigation of temporal and spatial variation of carbon monoxide in the southern hemisphere.

Abstract

Carbon monoxide (CO) is a colourless, odourless, and tasteless gas. It is also poisonous. CO is a trace gas in the Earth's atmosphere, with typical concentrations of the order of hundreds of parts per billion and a lifetime of 2 months. CO concentration, which is monitored by the Terra satellite, varies with location and time. This study focused on the Southern Hemisphere (SH), particularly South America, southern Africa and Australia, between 2005 and 2019. It had two aims: The rst was to investigate the sources and seasonal concentrations of CO over these regions, and to analyse whether meridional and zonal winds play a role in CO distribution. It is believed that biomass burning, both natural and anthropogenic, is responsible for the vast majority (99%) of CO emissions. This was tested by comparing distributions of burned areas and CO concentrations. Winter months had more burned areas than summer months, with an average burned area of 1:51 107 m2 compared to 8:19 106 m2. Total column CO concentrations measured by the MOPITT sensor were also found to be higher during winter and spring months. Over southern Africa CO levels reached 36 1017 mol=cm2 in winter, compared to 26 1017 mol=cm2 in summer. Correlation analysis using Pearson coe cients and p-values showed a general positive correlation between CO emissions and burned areas, supporting the earlier conjecture. Trend analysis showed a steady decline in CO concentrations over the study period, likely due to decreases in burned area. Overlaid maps supported the idea that winds play a role in CO distribution in the Southern Hemisphere. For example, westward CO transport from Africa to South America was observed in July- August close to the equator. Then in September-October at latitudes higher than 20° S, eastward transport from South America to southern Africa and from southern Africa to Australia was observed. The second aim of this study was to investigate whether El Ni~no/La Ni~na events played a part in the distributions of CO in the SH between 2005 and 2019. These events are climate patterns related to irregular warming/cooling of the ocean surface in the central and eastern tropical Paci c Ocean. A La Ni~na phase, an El Ni~no phase and an intermediate neutral phase were identi ed during the study period, and their CO distributions, burn areas and precipitation levels were compared. In the SH El Ni~no causes below-average rainfall and the drier conditions lead to increased burning and above-average CO levels. La Ni~na causes above-average rainfall and the wetter conditions lead to reduced burning and below-average CO levels. The neutral phase displayed near-average conditions as expected.