Acid neutralizing effect in rainwater collected at a tropical urban area (Central Valley, Costa Rica)
Description
We report on the chemical and the carbon isotopic composition of dissolved inorganic carbon (DIC) of rainwater collected between May and October 2020 in the Central Valley of Costa Rica. Precipitation samples were collected daily (N=55) and analyzed for major ions, DIC, and δ13CDIC.
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Precipitation samples (N= 55) were collected daily around 7:00-9:00 am and between May and October 2020, using a passive collector (Palmex Ltd., Croatia). Samples were filtered using 0.45 μm polytetrafluorethylene (PTFE) syringe membranes and fractionated into two portions: i) 30 mL were stored at dark and frozen conditions (-10°C) until isotopic analysis of dissolved inorganic carbon (δ13CDIC) and ii) 30 mL were stored at dark and cool conditions (5°C) until ion and alkalinity analysis at the Stable Isotopes Research Group facilities (Universidad Nacional, Costa Rica). The hydrogen ion activity (pH) and electrical conductivity were measured after sample collection using a Benchtop Multiparameter Meter Mi-180 (Milwaukee Instruments, USA). Hourly meteorological conditions were registered at the sampling site with a Vantage Pro2 weather station (Davis Instruments, Hayward, CA, USA). The concentration of major cations and anions in precipitation samples was analyzed using a Dionex Ion Chromatograph ICS 5000+ (Dionex, CA). The following chemical parameters were quantified: nitrate (NO3-), chloride (Cl-), sulphate (SO42-), ammonium (NH4+), sodium (Na+), calcium (Ca2+), potassium (K+), and magnesium (Mg2+). Filtered aliquots (6mL) were pipetted into Exetainer® vials. An automated DIC sample preparation system (Picarro AutoMate FX system, USA) was employed to inject a 10% phosphoric acid solution into each sealed vial to liberate CO2 from the sample. Additionally, a stream of dry and ultra-pure nitrogen was bubbled through the acidified solution to flush the released CO2 from the vial headspace. The CO2 was captured into gas sampling bags of a Picarro LiaisonTM Universal Interface before being analyzed using Cavity Ring Down Spectroscopy (CRDS, Picarro G2201-i).