Coastal water source of short‐lived halocarbons in New England

Abstract

[1] Short-lived halocarbon tracers were used to investigate marine influences on air quality in a coastal region of New England. Atmospheric measurements made at the University of New Hampshire's Observing Station at Thompson Farm (TF) in Durham, New Hampshire, indicate that relatively large amounts of halocarbons are emitted from local estuarine and coastal oceanic regions. Bromine-containing halocarbons of interest in this work include bromoform (CHBr 3 ) and dibromomethane (CH 2 Br 2 ). The mean mixing ratios of CHBr 3 and CH 2 Br 2 from 11 January to 5 March 2002 were 2.6 pptv and 1.6 pptv, and from 1 June to 31 August 2002 mean mixing ratios were 5.9 pptv and 1.4 pptv, respectively. The mean mixing ratio of CHBr 3 was not only highest during summer, but both CHBr 3 and CH 2 Br 2 exhibited large variability in their atmospheric mixing ratios during this season. We attribute the greater variability to increased production combined with faster atmospheric removal rates. Other seasonal characteristics of CHBr 3 and CH 2 Br 2 in the atmosphere, as well as the impact of local meteorology on their distributions at this coastal site, are discussed. Tetrachloroethene (C 2 Cl 4 ) and trichloroethene (C 2 HCl 3 ) were used to identify time periods influenced by urban emissions. Additionally, measurements of CHBr 3, CH 2 Br 2, C 2 Cl 4 , methyl iodide (CH 3 I), and ethyl iodide (C 2 H 5 I) were made at TF and five sites throughout the nearby Great Bay estuarine area between 18 and 19 August 2003. These measurements were used to elucidate the effect of the tidal cycle on the distributions of these gases. The mean mixing ratios of CHBr 3 , CH 2 Br 2 , CH 3 I, and C 2 H 5 I were $82%, 46%, 14%, and 17% higher, respectively, near the coast compared to inland sites, providing evidence for a marine source of short-lived halocarbons at TF. Correlation between the tidal cycle and atmospheric concentrations of marine tracers on the night of 18 August 2003 showed that the highest values for the brominated species occurred $2-3 hours after high tide. Emission fluxes of CHBr 3 , CH 2 Br 2 , CH 3 I, and C 2 H 5 I on this night were estimated to be 26 ± 57, 4.7 ± 5.4, 5.9 ± 4.6, and 0.065 ± 0.20 nmol m À2 h À1 , respectively. Finally, the anthropogenic source strength of CHBr 3 was calculated to determine its impact on atmospheric levels observed in this region. Although our results indicate that anthropogenic contributions could potentially range from 15 to 60% of the total dissolved CHBr 3 in the Great Bay, based on the observed ratio of CH 2 Br 2 /CHBr 3 and surface seawater measurements in the Gulf of Maine, it appears unlikely that anthropogenic activities are a significant source of CHBr 3 in the region.

Multi-year (2004–2008) record of nonmethane hydrocarbons and halocarbons in New England: seasonal variations and regional sources

“…A three gas chromatograph system equipped with two flame ionization detectors (FID), two electron capture detectors (ECD), and a mass spectrometer (MS) was used for analysis of each 1500 cc (STP) sample aliquot. The PLOT-FID, OV-1701-ECD, and OV-624-MS column-detector combinations have remained the same throughout 2004-2008 (see Sive et al (2005) and Zhou et al (2005Zhou et al ( , 2006Zhou et al ( , 2008 for additional information). In 2006, the FID channel used for C 4 -C 10 NMHC analysis was changed from a DB-1 column (60 m×0.32 mm I.D., 1 µm film thickness) to a VF-1ms column (60 m×0.32 mm I.D., 1 µm film thickness).…”

“…We followed a simple box model approach which has been effectively used in previous studies to calculate emission and removal rates of trace gases in this region (i.e., Talbot et al, 2005;Zhou et al, 2005;Sive et al, 2007;White et al, 2008;Russo et al, 2010). This method uses measurements made on nights with low wind speeds and when a stable inversion layer has developed because under these conditions, the exchange of air between the nocturnal boundary layer (NBL) and the residual layer above is limited (e.g., Hastie et al, 1993;Gusten et al, 1998;Talbot et al, 2005).…”

“…Multi-year VOC data published thus far includes measurements of C 1 -C 5 alkyl nitrates (Russo et al, 2010), methyl iodide , and oxygenated VOCs (OVOCs) and select NMHCs (Jordan et al, 2009). Summertime measurements (2002)(2003)(2004) of NMHCs, OVOCs, and marine-derived halocarbons at TF were discussed in Talbot et al (2005), Chen et al (2007), White et al (2008), and Zhou et al (2005Zhou et al ( , 2008. In this work, four years (2004)(2005)(2006)(2007)(2008) of ambient C 2 -C 8 NMHC and anthropogenic halocarbon data from daily canister samples collected at the Thompson Farm site in southeastern New Hampshire are presented and discussed.…”

Temporal variability, sources, and sinks of C<sub>1</sub>-C<sub>5</sub> alkyl nitrates in coastal New England

“…Previous research has shown that this area is influenced by marine, vegetative, and anthropogenic sources of nonmethane hydrocarbons (NMHCs) and halocarbons (Sive et al, 2007;Varner et al, 2008;White et al, 2008White et al, , 2009Zhou et al, 2005Zhou et al, , 2008 and is strongly impacted by boundary layer dynamics (Mao and Talbot, 2004a;. In this work, we characterize the seasonal and diurnal variability, sources, and sinks of C 1 -C 5 alkyl nitrates at an inland site (Thompson Farm) (Fig.…”

“…TF is surrounded by a mixed forest and is located ∼ 20 km inland from the Gulf of Maine, 5 km northwest of the Great Bay estuary, and ∼ 100 km north of Boston, MA. Samples were analyzed onsite by an in situ automated gas chromatography (GC) system equipped with two flame ionization detectors (FID) for detecting NMHCs and two electron capture detectors (ECD) for measuring halocarbons and alkyl nitrates (described in detail by Zhou et al, 2005. The measurement precision for each of the hydrocarbons, halocarbons, and alkyl nitrates ranged from 0.3-15%.…”