Compound-Specific Carbon Isotopic Composition of Ethanol in Brazil and US Vehicle Emissions and Wet Deposition.

Global atmospheric ethanol budget models include large uncertainties in the magnitude of ethanol emission sources and sinks. To apply stable isotope techniques to constrain ethanol emission sources, a headspace solid phase microextraction gas chromatograph-combustion-isotope ratio mass spectrometry method (HS-SPME-GC-C-IRMS) was developed to measure the carbon isotopic composition of aqueous phase ethanol at natural abundance levels (1-30 μM) with a precision of 0.4‰.

Variability of ethanol concentration in rainwater driven by origin versus season in coastal and inland North Carolina, USA.

Rainwater ethanol concentrations were measured for one year (June 2013-May 2014) in central (Elon, NC) and coastal (Wilmington, NC) North Carolina, allowing for a comparison of the effects of coastal and marine rain on ethanol concentration and deposition both at the coast and 250 km inland. Rain samples were collected on an event basis and analyzed using enzyme oxidation and headspace solid-phase microextraction (HS-SPME). The volume-weighted average ethanol concentration at Elon (609 ± 116 nM) was higher than at Wilmington (208 ± 21 nM).

Use of experimentally determined Henry's Law and salting-out constants for ethanol in seawater for determination of the saturation state of ethanol in coastal waters.

The Henry's law constant for ethanol in seawater was experimentally determined to be 221 ± 4 M/atm at 22 °C compared with 247 ± 6 M/atm in pure water. The salting out coefficient for ethanol was 0.13 M.

Surface waters as a sink and source of atmospheric gas phase ethanol.

This study reports the first ethanol concentrations in fresh and estuarine waters and greatly expands the current data set for coastal ocean waters. Concentrations for 153 individual measurements of 11 freshwater sites ranged from 5 to 598 nM. Concentrations obtained for one estuarine transect ranged from 56 to 77 nM and levels in five coastal ocean depth profiles ranged from 81 to 334 nM.

Temporal and spatial variability of trace volatile organic compounds in rainwater.

This study presents the first detailed concentration profile of trace VOCs in atmospheric waters. Analytes were detected and quantified in 111 unique rain events in Wilmington, NC, USA over a one-year period. Headspace solid phase microextraction was optimized for detection of these compounds at sub-nanomolar levels.

Characterization of carbohydrates in rainwater from the southeastern North Carolina.

Carbohydrates have been widely reported in atmospheric aerosols, but have not previously been quantified in rainwater. We have identified and quantified a series of 11 specific compounds including monosaccharides (glucose, fructose, arabinose, galactose and pinitol), disaccharides (sucrose and trehalose), sugar alcohols (arabitol, dulcitol and mannitol) and the anhydrosaccharide levoglucosan. Rainwater analyzed in this study includes 52 distinct precipitation events in Wilmington, NC between June 2011 and October 2012.

Controls on the redox potential of rainwater.

Hydrogen peroxide acting as a reductant affects the redox potential of rainwater collected at the Bermuda Atlantic Time Series Station, the South Island of New Zealand, the contiguous USA, and the primary study site in Wilmington, NC. Analytical measurements of both halves of redox couples for dissolved iron, mercury, and the nitrate-nitrite-ammonium system can predict the rainwater redox potential measured directly by a platinum electrode. Measurements of these redox couples along with the pH in rain yields pe⁻ between 8 and 11; the half reaction for hydrogen peroxide acting as a reductant using typical rainwater conditions of 15 μM H₂O₂ at pH 4.

Long-term temporal variability in hydrogen peroxide concentrations in Wilmington, North Carolina USA rainwater.

Measurements of hydrogen peroxide (H(2)O(2)), pH, dissolved organic carbon (DOC), and inorganic anions (chloride, nitrate, and sulfate) in rainwater were conducted on an event basis at a single site in Wilmington, NC for the past decade in a study that included over 600 individual rain events. Annual volume weighted average (VWA) H(2)O(2) concentrations were negatively correlated (p < 0.001) with annual VWA nonseasalt sulfate (NSS) concentrations in low pH (<5) rainwater.

Changing chemical composition of precipitation in Wilmington, North Carolina, U.S.A.: implications for the Continental U.S.A.

The H+(aq) concentration in Wilmington, NC, precipitation has decreased by approximately 50% during the preceding two decades, similar to trends seen nationwide. The decrease in acidity is important because solution pH plays a key role in atmospheric reactions, and because the change is so large. This study presents the first long-range study of dissolved organic carbon (DOC) levels in precipitation which demonstrates that DOC concentrations have decreased by approximately half in Wilmington, NC, precipitation.

Redox speciation of copper in rainwater: temporal variability and atmospheric deposition.

Copper speciation was determined in 68 rainwater samples collected in Wilmington, NC, from August 25, 2000, to September 24, 2002. Volume-weighted average concentrations of Cu(total), dissolved Cu(II), and dissolved Cu(I) were 5.3, 3.

Chromium speciation in rainwater: temporal variability and atmospheric deposition.

The concentrations of the various chromium species were determined in 89 rainwater samples collected in Wilmington, NC, from October 1, 1999, to December 31, 2001. Volume-weighted annual average concentrations of Cr(total), particulate Cr, Cr(III)(aq), and Cr(VI)(aq) were 4.6, 2.