Studies on CO variation and trends over South Africa and the Indian Ocean using TES satellite data

Abstract

In this study, we used measurements from the tropospheric emission spectrometer aboard the Earth Observing System's Aura satellite over South Africa, Madagascar and Reunion Island to investigate variations and trends in tropospheric carbon monoxide (CO) over 5 years, from 2005 to 2009, and at 47 pressure levels from 1000 hPa to 10 hPa. We believe that the study is the first of its kind to address the use of space-borne data for CO distribution over southern Africa. Maximum CO was recorded during spring and minimum during summer. Positive anomalies were identified in 2005 and 2007 during the spring and negative anomalies in the beginning of the year (especially in 2006, 2008 and 2009). The estimated trends based on a linear regression method on inter-annual distribution predicted a decreasing rate of 2.1% per year over South Africa, 1.8% per year over Madagascar and 1.7% per year over Reunion Island. The surface CO measurements made at Cape Point station (34.35°S, 18.48°E) showed an average decline of 0.1 ppb per month, which corresponded to 2.4% of the average annual mean for the studied period. The observed decrease in CO was linked to the La Niña event which occurred in 2006 and 2008 and a declining rate of biomass burning activity in the southern hemisphere over the observation period. TES measurements are in agreement with ground-based measurements and can be used with confidence to complement CO measurements for future analyses over the southern tropics and middle latitude.

Trend of atmospheric mercury concentrations at Cape Point for 1995–2004 and since 2007

“…Hg emissions from coal-fired power plants, the largest anthropogenic Hg source, tend to be nearly constant over the year (Rotty, 1987). However, biomass burning is a highly seasonal phenomenon with maximum emissions during August-September both in South America and southern Africa (Duncan et al, 2003;van der Werf et al, 2006). Taking into account a delay by ∼ 3 months due to intra-hemispherical air mixing time, OctoberNovember coincides with the maximum absolute seasonal trends: an upward one for 2007-2015 and a downward one for the 1995-2004 period.…”

“…As the emission estimates by Granier et al (2011) end in 2010, no trend in emissions from biomass burning in the 2007-2015 period can be given. Nonetheless, the ambient Cape Point CO data have shown a measurable decrease during 2003 till 2014 (Toihir et al, 2015). We tried to calculate seasonal trends of baseline CO mixing ratios for the 1995-June 2015 periods, but none of the trends was significant.…”

“…For the 2007-2015 period the highest upward trend was found in austral spring. Hg emissions from biomass burning in South America and southern Africa both peak in August and September (Duncan et al, 2003;van der Werf et al, 2006). Although the trend of these emissions is uncertain because of differences between different emission inventories (Granier et al, 2011), it can produce different trends in different seasons.…”

A review of four decades of atmospheric trace gas measurements at Cape Point, South Africa

“…At Cape Point, CO concentrations form a seasonal cycle with a maximum in winter (70-80 ppb) and minimum in austral summer (40-50 ppb;Seiler et al, 1984;Scheel et al, 1998). Reasons behind the maximum in winter may be two-fold, firstly, decreased reactions with ˙OH and secondly, an influx of CO from Cape Town carried on the northwesterly winds (Seiler et al, 1984;Toihir, 2015).…”

“…Other impacts might include changes in source and sink processes of various trace gases such as CO (Scheel et al, 1998;Toihir, 2015).…”