TITLE:
Near Surface Carbon Dioxide and Methane in Urban Areas of Costa Rica
AUTHORS:
Germain Esquivel-Hernández, Mario Villalobos-Forbes, Ricardo Sánchez-Murillo, Christian Birkel, Juan Valdés-González, Jan Boll
KEYWORDS:
Carbon Dioxide, Methane, Urban Areas, Costa Rica, HYSPLIT, Atmospheric Conditions
JOURNAL NAME:
Open Journal of Air Pollution,
Vol.4 No.4,
December
14,
2015
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.