Temporal variation, regional sources, and removal processes of volatile organic compounds in New England

This dissertation describes three research projects with the common objective of characterizing the influence of volatile organic compounds (VOCs) on air quality in New England using measurements made over multiple years (2002-2008) and from different sampling locations. The specific objectives include identifying sources (direct emission or secondary production), quantifying mixing ratios, and characterizing the chemical (i.e., oxidation, photolysis) and physical (i.e., transport, mixing) processes which regulate the distributions of VOCs in the troposphere over southeastern New Hampshire. Chapters 2 and 3 discuss the seasonal and interannual variability of nonmethane hydrocarbons (NMHCs), selected halocarbons, and alkyl nitrates using measurements from canister samples collected at Thompson Farm in Durham, NH throughout January 2004-February 2008. Several anthropogenic and biogenic sources of NMHCs and halocarbons were identified based on correlations with tracer compounds and comparisons with source signatures. Additionally, evidence for the dry deposition of alkyl nitrates of night was observed which is a previously unaccounted for removal mechanism. Analysis of alkyl nitrate/parent hydrocarbon ratios, measurements made onboard the NOAA R/V Ronald H. Brown during the 2002 New England Air Quality Study, and canister samples collected throughout the Great Bay estuary in August 2003 are presented to assess the relative contributions of anthropogenic and marine sources of alkyl nitrates. The research described in Chapter 4 used measurements of VOCs made at an inland (Thompson Farm) and an offshore (Appledore Island) site to identify evidence of chlorine initiated oxidation of VOCs, estimate chlorine atom (Cl) concentrations during two summers and for different transport sectors, and assess the potential influence of chlorine chemistry on the oxidative capacity of the troposphere over coastal New Hampshire. Comparable Cl concentrations were estimated using a novel technique based on the lifetime-variability relationship of NMHCs and using the traditional NMHC ratio method. Furthermore, the daytime loss of DMS and ethane in the marine sector of AI was reproduced when reaction with both OH and Cl were considered providing supporting evidence for Cl chemistry occurring in this region

Estimates of Cl atom concentrations and hydrocarbon kinetic reactivity in surface air at Appledore Island, Maine (USA), during International Consortium for Atmospheric Research on Transport and Transformation/Chemistry of Halogens at the Isles of Shoals

Average hydroxyl radical (OH) to chlorine atom (Cl·) ratios ranging from 45 to 119 were determined from variability‐lifetime relationships for selected nonmethane hydrocarbons (NMHC) in surface air from six different transport sectors arriving at Appledore Island, Maine, during July 2004. Multiplying these ratios by an assumed average OH concentration of 2.5 × 106 cm−3 yielded estimates of Cl· concentrations of 2.2 to 5.6 × 104 cm−3. Summed reaction rates of methane and more than 30 abundant NMHCs with OH and Cl· suggest that Cl· reactions increased the kinetic reactivity of hydrocarbons by 16% to 30% over that due to OH alone in air associated with the various transport sectors. Isoprene and other abundant biogenic alkenes were the most important hydrocarbon contributors after methane to overall kinetic reactivity

Carbonyl sulfide exchange in a temperate loblolly pine forest grown under ambient and elevated CO2

Vegetation, soil and ecosystem level carbonyl sulfide (COS) exchange was observed at Duke Forest, a temperate loblolly pine forest, grown under ambient (Ring 1, R1) and elevated (Ring 2, R2) CO2. During calm meteorological conditions, ambient COS mixing ratios at the top of the forest canopy followed a distinct diurnal pattern in both CO2 growth regimes, with maximum COS mixing ratios during the day (R1=380±4 pptv and R2=373±3 pptv, daytime mean ± standard error) and minimums at night (R1=340±6 pptv and R2=346±5 pptv, nighttime mean ± standard error) reflecting a significant nighttime sink. Nocturnal vegetative uptake (−11 to −21 pmol m−2s−1, negative values indicate uptake from the atmosphere) dominated nighttime net ecosystem COS flux estimates (−10 to −30 pmol m−2s−1) in both CO2 regimes. In comparison, soil uptake (−0.8 to −1.7 pmol m−2 s−1) was a minor component of net ecosystem COS flux. In both CO2 regimes, loblolly pine trees exhibited substantial COS consumption overnight (50% of daytime rates) that was independent of CO2 assimilation. This suggests current estimates of the global vegetative COS sink, which assume that COS and CO2 are consumed simultaneously, may need to be reevaluated. Ambient COS mixing ratios, species specific diurnal patterns of stomatal conductance, temperature and canopy position were the major factors influencing the vegetative COS flux at the branch level. While variability in branch level vegetative COS consumption measurements in ambient and enhanced CO2 environments could not be attributed to CO2 enrichment effects, estimates of net ecosystem COS flux based on ambient canopy mixing ratio measurements suggest less nighttime uptake of COS in R2, the CO2 enriched environment

Coastal water source of short‐lived halocarbons in New England

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\u27s 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 (CHBr3) and dibromomethane (CH2Br2). The mean mixing ratios of CHBr3 and CH2Br2 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 CHBr3 was not only highest during summer, but both CHBr3 and CH2Br2 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 CHBr3 and CH2Br2 in the atmosphere, as well as the impact of local meteorology on their distributions at this coastal site, are discussed. Tetrachloroethene (C2Cl4) and trichloroethene (C2HCl3) were used to identify time periods influenced by urban emissions. Additionally, measurements of CHBr3, CH2Br2, C2Cl4, methyl iodide (CH3I), and ethyl iodide (C2H5I) 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 CHBr3, CH2Br2, CH3I, and C2H5I 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 CHBr3, CH2Br2, CH3I, and C2H5I on this night were estimated to be 26 ± 57, 4.7 ± 5.4, 5.9 ± 4.6, and 0.065 ± 0.20 nmol m−2 h−1, respectively. Finally, the anthropogenic source strength of CHBr3 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 CHBr3 in the Great Bay, based on the observed ratio of CH2Br2/CHBr3 and surface seawater measurements in the Gulf of Maine, it appears unlikely that anthropogenic activities are a significant source of CHBr3 in the region

Controls on atmospheric chloroiodomethane (CH2ClI) in marine environments

Mixing ratios of chloroiodomethane (CH2ClI) in ambient air were quantified in the coastal North Atlantic region (Thompson Farm, Durham, New Hampshire, and Appledore Island, Maine) and two remote Pacific areas (Christmas Island, Kiribati, and Oahu, Hawaii). Average mixing ratios were 0.15 ± 0.18 and 0.68 ± 0.66 parts per trillion by volume (pptv) at Thompson Farm and Appledore Island, respectively, compared to 0.10 ± 0.05 pptv at Christmas Island and 0.04 ± 0.02 pptv in Hawaii. Photolysis constrained the daytime mixing ratios of CH2ClI at all locations with the minimum occurring at 1600 local time. Daily average fluxes to the atmosphere were estimated from mixing ratios and loss due to photolysis at Appledore Island, Christmas Island and Hawaii, and were 58 ± 9, 19 ± 3, and 5.8 ± 1.0 nmol CH2ClI m−2 d−1, respectively. The measured sea‐to‐air flux from seawater equilibrator samples obtained near Appledore Island was 6.4 ± 2.9 nmol CH2ClI m−2 d−1. Mixing ratios of CH2ClI at Appledore Island increased with increasing wind speed. The maximum mixing ratios observed at Thompson Farm (1.6 pptv) and Appledore Island (3.4 pptv) are the highest reported values to date, and coincided with high winds associated with the passage of Tropical Storm Bonnie. We estimate that high winds during the 2004 hurricane season increased the flux of CH2ClI from the North Atlantic Ocean by 8 ± 2%

Bromoform and dibromomethane measurements in the seacoast region of New Hampshire, 2002–2004

Atmospheric measurements of bromoform (CHBr3) and dibromomethane (CH2Br2) were conducted at two sites, Thompson Farm (TF) in Durham, New Hampshire (summer 2002–2004), and Appledore Island (AI), Maine (summer 2004). Elevated mixing ratios of CHBr3 were frequently observed at both sites, with maxima of 37.9 parts per trillion by volume (pptv) and 47.4 pptv for TF and AI, respectively. Average mixing ratios of CHBr3 and CH2Br2 at TF for all three summers ranged from 5.3–6.3 and 1.3–2.3 pptv, respectively. The average mixing ratios of both gases were higher at AI during 2004, consistent with AI\u27s proximity to sources of these bromocarbons. Strong negative vertical gradients in the atmosphere corroborated local sources of these gases at the surface. At AI, CHBr3 and CH2Br2 mixing ratios increased with wind speed via sea‐to‐air transfer from supersaturated coastal waters. Large enhancements of CHBr3 and CH2Br2 were observed at both sites from 10 to 14 August 2004, coinciding with the passage of Tropical Storm Bonnie. During this period, fluxes of CHBr3 and CH2Br2 were 52.4 ± 21.0 and 9.1 ± 3.1 nmol m−2 h−1, respectively. The average fluxes of CHBr3 and CH2Br2 during nonevent periods were 18.9 ± 12.3 and 2.6 ± 1.9 nmol m−2 h−1, respectively. Additionally, CHBr3 and CH2Br2 were used as marine tracers in case studies to (1) evaluate the impact of tropical storms on emissions and distributions of marine‐derived gases in the coastal region and (2) characterize the transport of air masses during pollution episodes in the northeastern United States

Are biogenic emissions a significant source of summertime atmospheric toluene in the rural Northeastern United States?

Summertime atmospheric toluene enhancements at Thompson Farm in the rural northeastern United States were unexpected and resulted in a toluene/benzene seasonal pattern that was distinctly different from that of other anthropogenic volatile organic compounds. Consequently, three hydrocarbon sources were investigated for potential contributions to the enhancements during 2004–2006. These included: (1) increased warm season fuel evaporation coupled with changes in reformulated gasoline (RFG) content to meet US EPA summertime volatility standards, (2) local industrial emissions and (3) local vegetative emissions. The contribution of fuel evaporation emission to summer toluene mixing ratios was estimated to range from 16 to 30 pptv d−1, and did not fully account for the observed enhancements (20–50 pptv) in 2004–2006. Static chamber measurements of alfalfa, a crop at Thompson Farm, and dynamic branch enclosure measurements of loblolly pine trees in North Carolina suggested vegetative emissions of 5 and 12 pptv d−1 for crops and coniferous trees, respectively. Toluene emission rates from alfalfa are potentially much larger as these plants were only sampled at the end of the growing season. Measured biogenic fluxes were on the same order of magnitude as the influence from gasoline evaporation and industrial sources (regional industrial emissions estimated at 7 pptv d−1 and indicated that local vegetative emissions make a significant contribution to summertime toluene enhancements. Additional studies are needed to characterize the variability and factors controlling toluene emissions from alfalfa and other vegetation types throughout the growing season

Volatile organic compounds in northern New England marine and continental environments during the ICARTT 2004 campaign

Volatile organic compound (VOC) measurements were made during the summer 2004 International Consortium for Atmospheric Research on Transport and Transformation (ICARTT) at Thompson Farm (TF), a continental site 25 km from the New Hampshire coast, and Appledore Island (AI), a marine site 10 km off the Maine coast. The 24 h mean total hydroxyl radical (OH) reactivity (±1σ) for the suite of VOCs was 4.15 (±2.64) s−1 at TF and 2.57 (±1.10) s−1 at AI. The larger range of reactivity at TF was dominated by isoprene and the monoterpenes (mean combined reactivity = 2.01 (±2.57) s−1). The impact of local anthropogenic hydrocarbon sources such as liquefied petroleum gas (LPG) leakage and fossil fuel evaporation was evident at both sites. During the campaign, a propane flux of 9 (±2) × 109 molecules cm−2 s−1 was calculated from the linear regression of the mean 0100–0400 local time mixing ratios at TF. This is consistent with fluxes observed in 2003 at sites spread throughout the coastal area of New Hampshire indicating that LPG tank leakage is a major hydrocarbon source throughout the region. Net monoterpene fluxes during ICARTT at TF were 6 (±2), 1.8 (±0.4), 1.2 (±0.6), and 0.4 (±0.5) × 109 molecules cm−2 s−1 for α‐pinene, β‐pinene, camphene, and limonene, respectively. Comparison to estimated NO3 and O3 loss rates indicate that gross monoterpene emission rates were approximately double the observed net fluxes at TF and comparable to current monoterpene nighttime emission inventory estimates for the northeast

Maternal Dioxin Exposure Combined with a Diet High in Fat Increases Mammary Cancer Incidence in Mice

BackgroundRESULTS from previous studies have suggested that breast cancer risk correlates with total lifetime exposure to estrogens and that early-life 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) exposure or diets high in fat can also increase cancer risk.ObjectivesBecause both TCDD and diet affect the estrogen pathway, we examined how TCDD and a high-fat diet (HFD) interact to alter breast cancer susceptibility.MethodsWe exposed pregnant female FVB/NJ mice (12.5 days postcoitus) to 1 microg/kg TCDD or vehicle; at parturition, the dams were randomly assigned to a low-fat diet (LFD) or a high-fat diet (HFD). Female offspring were maintained on the same diets after weaning and were exposed to 7,12-dimethylbenz[a]anthracene on postnatal days (PNDs) 35, 49, and 63 to initiate mammary tumors. A second cohort of females was treated identically until PND35 or PND49, when mammary gland morphology was examined, or PND50, when mammary gland mRNA was analyzed.ResultsWe found that maternal TCDD exposure doubled mammary tumor incidence only in mice fed the HFD. Among HFD-fed mice, maternal TCDD exposure caused rapid mammary development with increased Cyp1b1 (cytochrome P450 1B1) expression and decreased Comt (catechol-O-methyltransferase) expression in mammary tissue. Maternal TCDD exposure also increased mammary tumor Cyp1b1 expression.ConclusionsOur data suggest that the HFD increases sensitivity to maternal TCDD exposure, resulting in increased breast cancer incidence, by changing metabolism capability. These results provide a mechanism to explain epidemiological data linking early-life TCDD exposure and diets high in fat to increased risk for breast cancer in humans