Abstract
Little information is available for Central America regarding methane and carbon dioxide mixing ratios in urban areas. This work reports a representative spatial and seasonal study of near surface carbon dioxide and methane, carried out between July 2014 and January 2015 (27 weeks) in the Central Valley of Costa Rica, and other urban and rural sites across the country and covering three distinct seasons: Mid-summer drought (July-August), wet season (September-November) and transition period (December-January). The mixing ratios of both gases are clearly influenced by the metropolitan area, and by the prevailing atmospheric conditions during the wet season months. Average carbon dioxide concentration (629 ± 80 ppm) and average methane concentration (2192 ± 110 ppb) were up to 8% and up to 10%, respectively, higher during the wet season than the values recorded outside this period. HYSPLIT back air mass trajectories analysis, and weather data available for the Central Valley, suggest that these differences arise as result of a reduction in the mixing layer of depth (~425 m) and the wind speed (~1.5 m/s) across the valley, favoring the accumulation of polluted air masses in the metropolitan area. Other natural and anthropogenic sources, like the volcanic emissions of the Turrialba Volcano and the livestock activities at rural sites, apparently influence the mixing ratios of both gases across Costa Rica. Although the scope of this study is limited to representative seasonal conditions of the Central Valley in 2014 and 2015, it is possible considering the information presented in this work that the “dome” phenomenon can be assumed to exist.
Highlights
For more than 50 years, the atmospheric monitoring done at Mauna Loa, Hawaii, and the South Pole, has allowed scientists to track greenhouse and other trace gases in the global atmosphere [1] [2]
The present data were gathered during a representative seasonal investigation of near surface CH4 and CO2, based on the analysis of samples collected at weekly intervals during July 2014-January 2015 at six locations, in order to 1) investigate the seasonal influence on CO2 and CH4 concentrations in the metropolitan area and surrounding areas inside the Central Valley, in combination with Hybrid Single Particle Lagrangian Integrated Trajectory model (HYSPLIT) back air mass trajectory analysis, and 2) compare the CO2 and CH4 levels with other urban, rural and protected areas located across the continental divide of the country
The CO2 and CH4 mixing ratios recorded at the Central Valley sampling sites are shown in Figure 3 and Figure 4, respectively, which compare sampling sites located inside the metropolitan area with those located outside the urban conglomerate
Summary
For more than 50 years, the atmospheric monitoring done at Mauna Loa, Hawaii, and the South Pole, has allowed scientists to track greenhouse and other trace gases in the global atmosphere [1] [2]. The present data were gathered during a representative seasonal investigation of near surface CH4 and CO2, based on the analysis of samples collected at weekly intervals during July 2014-January 2015 at six locations, in order to 1) investigate the seasonal influence on CO2 and CH4 concentrations in the metropolitan area and surrounding areas inside the Central Valley, in combination with HYSPLIT back air mass trajectory analysis, and 2) compare the CO2 and CH4 levels with other urban, rural and protected areas located across the continental divide of the country These data can be used to address potential future changes of GHG emissions in urban conglomerates like the metropolitan area of Costa Rica, which may have a significant impact on the strength and distribution of major GHG emissions, in particular CO2, into the atmosphere in tropical regions like Central America. The population living in these urban areas is ~550,000 inhabitants, with an average density ~170 inhabitants per km
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