Temporal variability, sources, and sinks of Csub1/sub-Csub5/sub alkyl nitrates in coastal New England

摘要

Seven C₁-C₅ alkyl nitrates were measured both on the mainland andoff the coast of New Hampshire using gas chromatographic techniques. Fiveseparate data sets are presented to characterize the seasonal and diurnaltrends and the major sources and loss processes of these compounds. Based onin situ measurements conducted at the University of New Hampshire (UNH)Atmospheric Observing Station at Thompson Farm (TF) located in southeast NHduring winter (January–February) 2002, summer (June–August) 2002, summer(July–August) 2004, and on daily canister samples collected at midday fromJanuary 2004–February 2008, the median total alkyl nitrate mixing ratio(ΣRONO₂) was 23–25 pptv in winter and 14–16 pptv in summer.During summers 2002 and 2004, MeONO₂ decreased overnight and reachedminimum hourly average mixing ratios in the early morning. Comparison withwind speed and trace gas trends suggested that dry deposition contributed tothe early morning MeONO₂ minimum which is a previously unaccounted forremoval mechanism. The mean dry deposition rate and velocity of MeONO₂was estimated to be −0.5 nmol m−2 hr−1 and 0.13 cm s−1,respectively. Results from ambient air and surface seawater measurementsmade onboard the NOAA R/V Ronald H. Brown in the Gulf of Maine during the 2002 New EnglandAir Quality Study and from ambient canister samples collected throughout theGreat Bay estuary in August 2003 are also presented. Comparisons between thealkyl nitrate trends with anthropogenic and marine tracers suggest that amarine source of alkyl nitrates is not significant in coastal New England.Given the apparent prominence of a secondary source, comparisons betweenobserved and predicted alkyl nitrate/parent hydrocarbon ratios were madewhich demonstrated that background mixing ratios have a continuous andprevalent influence on the alkyl nitrate distribution.