The location of Costa Rica on the Central American Isthmus creates unique microclimate systems that receive moisture inputs directly from the Caribbean Sea and the Pacific Ocean. In Costa Rica, stable isotope monitoring was conducted by the International Atomic Energy Agency and the World Meteorological Association as part of the worldwide effort entitled Global Network of Isotopes in Precipitation. Sampling campaigns were mainly comprised of monthly-integrated samples during intermittent years from 1990 to 2005. The main goal of this study was to determine spatial and temporal isotopic variations of meteoric waters in Costa Rica using historic records. Samples were grouped in four main regions: Nicoya Peninsula ( 2 H = 6.65 18 O − 0.13; r 2 = 0.86); Pacific Coast ( 2 H = 7.60 18 O + 7.95; r 2 = 0.99); Caribbean Slope ( 2 H = 6.97 18 O + 4.97; r 2 = 0.97); and Central Valley ( 2 H = 7.94 18 O + 10.38; r 2 = 0.98). The water meteoric line for Costa Rica can be defined as  2 H = 7.61 18 O + 7.40 (r 2 = 0.98). The regression of precipitation amount and annual arithmetic means yields a slope of −1.6‰  18 O per 100 mm of rain (r 2 = 0.57) which corresponds with a temperature effect of −0.37‰  18 O/˚C. A strong correlation (r 2 = 0.77) of −2.0‰  18 O per km of elevation was found. Samples within the Nicoya Peninsula and Caribbean lowlands appear to be dominated by evaporation enrichment as shown in d-excess interpolation, especially during the dry months, likely resulting from small precipitation amounts. In the inter-mountainous region of the Central Valley and Pacific slope, complex moisture recycling processes may dominate isotopic variations. Generally, isotopic values tend to be more depleted as the rainy season progresses over the year. Air parcel back trajectories indicate that enriched isotopic compositions both in Turrialba and Monteverde are related to central Caribbean parental moisture and low rainfall intensities. Depleted events appear to be related to high rainfall amounts despite the parental origin of the moisture.

A great interest has arisen in establishing the impact of organic compounds on human health and air quality, especially those compounds emitted by automotive traffic. Knowledge of urban air pollutant concentrations is essential for the determination of exposure levels. With this information public health problems can be avoided and emissions sources can be identified. MTBE is one of such compound because of its effects both to the environment and to humans. In Costa Rica, as in many other parts of the world, MTBE has been added to gasoline up to 10% v/v. This study investigates ambient air concentration of MTBE in San Jose, Costa Rica. Samples were collected during OctoberDecember 2005 using Carbotrap ® cartridges and analyzed by thermal desorption combined with capillary gas chromatography. MTBE levels ranged from < 0.1 to 7.0 ppbv, with the highest concentrations observed in the wet season's months (May to November). The highways and industrial areas were identified as MTBE's point sources, both related with vehicle emissions. High levels of MTBE were also found in the vicinity of a gas station. These values represent the first measurements made in a Central American location, but are similar to those reported in other urban areas. The MTBE ambient air levels in San Jose, Costa Rica were not known until this study in 2005.

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.

Se determinó la concentración de seis aldehídos en muestras de aire, durante abril-junio de 2015, en la Reserva Biológica Monteverde (RBM) y en Heredia, Costa Rica. El formaldehído, el acetaldehído, el propanal, el butanal, el hexanal y el heptanal se tomaron con cartuchos de adsorción recubiertos con una disolución de la 2,4-dinitrofenilhidrazina (2,4-DNFH) y se analizaron por HPLC con un detector ultravioleta visible. Las concentraciones promedio de cada aldehído en Heredia se encontraron entre 12,78 µg/m3 y 72,57 µg/m3 durante la época seca y entre 7,95 µg/m3y 62,30 µg/m3 durante la transición a la época lluviosa; mientras que en la RBM las concentraciones encontradas estuvieron entre 1,93 µg/m3 y 22,62 µg/m3 durante la época seca y entre 0,26 µg/m3 y 4,68 µg/m3 durante la transición a la época lluviosa. La concentración total de los carbonilos en Heredia fue de 241,08 µg/m3 en la época seca y de 172,95 µg/m3 en la transición a la época lluviosa; esto, debido al efecto de dilución de contaminantes que hacen las lluvias y que la actividad fotoquímica es mayor en la época seca que en la transición a la época lluviosa. La concentración total de los carbonilos en la RBM fue de 42,07 µg/m3 en la época seca y de 13,47 µg/m3 en la transición a la época lluviosa.

This study reports the benzene exposure levels of commuters traveling within the metropolitan area of Costa Rica using personal cars, buses, and urban trains. 47 in-vehicle samples were collected in the 2014 wet season under three different driving conditions: rush hour traffic, normal traffic and weekends. Samples were collected in Tedlar bags and analyzed using 75 µm carboxenpolydimethylsiloxane (CAR/PDMS) and gas chromatography with flame ionization detection (GC-FID). Additionally, duplicate samples were collected on adsorption tubes filled with Tenax TA and analyzed by thermal desorption (TD) and GC-FID. Results indicate that travelling in cars and buses under rush hour conditions exposes commuters to statistically equal average benzene concentration of 48.7 and 51.6 µg/m 3 , respectively. Average benzene levels in urban trains (33.0 µg/m 3) were measured only during morning rush hours. Greater benzene levels in buses than personal cars concentrations may be attributable to the immersion of traffic-related emission within the bus cabins. Factors, such as the driving pattern, the number of vehicles on the route, the road infrastructure, and the prevalence of gasoline-fueled vehicles in Costa Rica, may increase ambient benzene concentrations. Benzene levels inside car cabins reported in this study are in the range of those reported in other urban areas; however, the corresponding concentrations inside buses and urban trains (rush hour only) are higher than previously published exposure levels.