Abstract. Multi-year time series records of C 2 -C 6 alkanes, C 2 -C 4 alkenes, ethyne, isoprene, C 6 -C 8 aromatics, trichloroethene (C 2 HCl 3 ), and tetrachloroethene (C 2 Cl 4 ) from canister samples collected during January 2004-February 2008 at the University of New Hampshire (UNH) AIRMAP Observatory at Thompson Farm (TF) in Durham, NH are presented. The objectives of this work are to identify the sources of nonmethane hydrocarbons (NMHCs) and halocarbons observed at TF, characterize the seasonal and interannual variability in ambient mixing ratios and sources, and estimate regional emission rates of NMHCs. Analysis of correlations and comparisons with emission ratios indicated that a ubiquitous and persistent mix of emissions from several anthropogenic sources is observed throughout the entire year. The highest C 2 -C 8 anthropogenic NMHC mixing ratios were observed in mid to late winter. Following the springtime minimums, the C 3 -C 6 alkanes, C 7 -C 8 aromatics, and C 2 HCl 3 increased in early to mid summer, presumably reflecting enhanced evaporative emissions. Mixing ratios of C 2 Cl 4 and C 2 HCl 3 decreased by 0.7±0.2 and 0.3±0.05 pptv/year, respectively, which is indicative of reduced usage and emissions of these halogenated solvents. Emission rates of C 3 -C 8 NMHCs were estimated to be 10 9 to 10 10 molecules cm −2 s −1 in winter 2006. The emission rates extrapolated to the state of New Hampshire and New England were ∼2-60 Mg/day and ∼12-430 Mg/day, respectively. Emission rates of benzene, toluene, ethylbenzene, Correspondence to: R. S. Russo (rrusso@gust.sr.unh.edu) xylenes, and ethyne in the 2002 and 2005 EPA National Emissions Inventories were within ±50% of the TF emission rates.

Abstract. 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][2005][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][2005][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.

[1] 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 (±1s) for the suite of VOCs was 4.15 (±2.64) s À1 at TF and 2.57 (±1.10) s À1 at AI. The larger range of reactivity at TF was dominated by isoprene and the monoterpenes (mean combined reactivity = 2.01 (±2.57) s À1 ). 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) Â 10 9 molecules cm À2 s À1 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) Â 10 9 molecules cm À2 s À1 for a-pinene, b-pinene, camphene, and limonene, respectively. Comparison to estimated NO 3 and O 3 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.

Abstract. 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) CO 2 . During calm meteorological conditions, ambient COS mixing ratios at the top of the forest canopy followed a distinct diurnal pattern in both CO 2 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 −2 s −1 , negative values indicate uptake from the atmosphere) dominated nighttime net ecosystem COS flux estimates (−10 to −30 pmol m −2 s −1 ) in both CO 2 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 CO 2 regimes, loblolly pine trees exhibited substantial COS consumption overnight (50% of daytime rates) that was independent of CO 2 assimilation. This suggests current estimates of the global vegetative COS sink, which assume that COS and CO 2 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 CO 2 environments could not be attributed to CO 2 enrichment effects, estimates of net ecosystem COS flux based on ambient canopy mixing ratio measurements suggest less nighttime uptake of COS in R2, the CO 2 enriched environment.

Abstract. Multi-year time series records of C2-C6 alkanes, C2-C4 alkenes, ethyne, isoprene, C6-C8 aromatics, trichloroethene (C2HCl3), and tetrachloroethene (C2Cl4) from canister samples collected during January 2004–February 2008 at the University of New Hampshire (UNH) AIRMAP Observatory at Thompson Farm (TF) in Durham, NH are presented. The objectives of this work are to identify the sources of nonmethane hydrocarbons (NMHCs) and halocarbons observed at TF, characterize the seasonal and interannual variability in ambient mixing ratios and sources, and estimate regional emission rates of NMHCs. Analysis of correlations and comparisons with emission ratios indicated that a ubiquitous and persistent mix of emissions from several anthropogenic sources is observed throughout the entire year. The highest C2-C8 anthropogenic NMHC mixing ratios were observed in mid to late winter. Following the springtime minimums, the C3-C6 alkanes, C7-C8 aromatics, and C2HCl3 increased in early to mid summer, presumably reflecting enhanced evaporative emissions. Mixing ratios of C2Cl4 and C2HCl3 decreased by 0.7±0.2 and 0.3±0.05 pptv/year, respectively, which is indicative of reduced usage and emissions of these halogenated solvents. Emission rates of C3-C8 NMHCs were estimated to be 109 to 1010 molecules cm-2 s-1 in winter 2006. The emission rates extrapolated to the state of New Hampshire and New England were ~2–60 Mg/day and ~12–430 Mg/day, respectively. The 2002 and 2005 EPA National Emissions Inventory (NEI) emission rates of benzene, ethylbenzene, and xylenes for New Hampshire agreed within ±<5–20% of the emission rates estimated from the TF data, while toluene emissions were overestimated (20–35%) in both versions of the NEI.