Near Surface Carbon Dioxide and Methane in Urban Areas of Costa Rica

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.

Stable Isotopic Characterization of Nitrate Wet Deposition in the Tropical Urban Atmosphere of Costa Rica

“…October when the influence of the ITCZ intensifies precipitation but also reduces wind speed across the Central Valley, which in turns enhances the wet deposition of NO3and SO4 -2 and acidifies the precipitation (Esquivel-Hernández et al 2015). As for the ion composition, our data agree well with the available information that reported SO4 2among the most abundant ions, but also a high correlation with NO3and NH4 + indicating a common anthropogenic origin (Herrera et al 2009).…”

Stable isotopic characterization of nitrate wet deposition in the tropical urban atmosphere of Costa Rica

“…As for our study, the pH range was relatively higher with most samples falling between 4.9 and 6.3 and only ~13% of these samples had pH values greater than 7. Overall, most low pH values were found in September and October when the influence of the ITCZ intensifies precipitation but also reduces wind speed across the Central Valley, which in turns enhances the wet deposition of NO3and SO4 -2 and acidifies the precipitation (Esquivel-Hernández et al 2015). As for the ion composition, our data agree well with the available information that reported SO4 2among the most abundant ions, but also a high correlation with NO3and NH4 + indicating a common anthropogenic origin (Herrera et al 2009).…”

“…The accumulation of air pollutants is enhanced during the wet season by a reduction in the mixed layer height, which decreases the intensity of the gas mixing dynamics in the local atmospheric boundary layer (Carballo-Chaves et al 2020;Esquivel-Hernández et al 2015). The chemical composition of precipitation collected in the capital city (San José) is also affected by contributions from these anthropogenic emissions (e.g., NOx and SO2) during the wet season (Herrera-Murillo and Rodríguez-Román 2009).…”