Abstract
Abstract. Seven C1-C5 alkyl nitrates were measured both on the mainland and off the coast of New Hampshire using gas chromatographic techniques. Five separate data sets are presented to characterize the seasonal and diurnal trends and the major sources and loss processes of these compounds. Based on in situ measurements conducted at the University of New Hampshire (UNH) Atmospheric Observing Station at Thompson Farm (TF) located in southeast NH during winter (January–February) 2002, summer (June–August) 2002, summer (July–August) 2004, and on daily canister samples collected at midday from January 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 reached minimum hourly average mixing ratios in the early morning. Comparison with wind speed and trace gas trends suggested that dry deposition contributed to the early morning MeONO2 minimum which is a previously unaccounted for removal mechanism. The mean dry deposition rate and velocity of MeONO2 was estimated to be −0.5 nmol m−2 hr−1 and 0.13 cm s−1, respectively. Results from ambient air and surface seawater measurements made onboard the NOAA R/V Ronald H. Brown in the Gulf of Maine during the 2002 New England Air Quality Study and from ambient canister samples collected throughout the Great Bay estuary in August 2003 are also presented. Comparisons between the alkyl nitrate trends with anthropogenic and marine tracers suggest that a marine source of alkyl nitrates is not significant in coastal New England. Given the apparent prominence of a secondary source, comparisons between observed and predicted alkyl nitrate/parent hydrocarbon ratios were made which demonstrated that background mixing ratios have a continuous and prevalent influence on the alkyl nitrate distribution.
Highlights
Alkyl nitrates are secondary products of hydrocarbon (RH) oxidation in the presence of nitrogen oxides (NOx=nitric oxide (NO)+NO2) and represent a link between the atmospheric carbon and nitrogen cycles (Reactions 1–4)
The samples were returned to the laboratory at University of New Hampshire (UNH) for analysis on a three gas chromatography (GC) system equipped with 2 flame ionization detectors (FID), 2 electron capture detectors (ECD), and a mass spectrometer (MS)
This illustrates that the development and dissipation of the nocturnal boundary layer (NBL) can contribute to the C1-C5 alkyl nitrate trends observed at Thompson Farm (TF) in both winter and summer
Summary
Alkyl nitrates are secondary products of hydrocarbon (RH) oxidation in the presence of nitrogen oxides (NOx=NO+NO2) and represent a link between the atmospheric carbon and nitrogen cycles (Reactions 1–4). The monofunctional alkyl nitrates typically comprise less than 10% of NOy because of the close proximity to primary NOx emissions (e.g., Shepson et al, 1993; Flocke et al, 1998; Thornberry et al, 2001; Simpson et al, 2006) They may constitute a much larger proportion of NOy in remote regions, such as the equatorial marine boundary layer (20–80%) (Talbot et al, 2000; Blake et al, 2003a) or the Arctic (∼10-20%) (Muthuramu et al, 1994). Research on the contribution of organic nitrogen to atmospheric nitrogen deposition and the impact on ecosystem functioning has been gaining importance (Cornell et al, 2003) In addition to their secondary photochemical source, primary emissions of light alkyl nitrates from the ocean (Atlas et al, 1993; Chuck et al, 2002; Moore and Blough, 2002; Blake et al, 2003a) and biomass burning have been observed. We incorporate data from a one day intensive study throughout the Great Bay estuary in August 2003 and daily canister samples collected during 2004–2008 at Thompson Farm in order to further describe the temporal variability and atmospheric distribution of alkyl nitrates
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