Observations of reactive nitrogen oxide fluxes by eddy covariance above two midlatitude North American mixed hardwood forests

Abstract

Abstract. Significant knowledge gaps persist in the understanding of forest-atmosphere exchange of reactive nitrogen oxides, partly due to a lack of direct observations. Chemical transport models require representations of dry deposition over a variety of land surface types, and the role of canopy exchange of NO x (= NO + NO 2 ) is highly uncertain. Biosphere-atmosphere exchange of NO x and NO y (= NO x + HNO 3 + PANs + RONO 2 + pNO − 3 + . . . ) was measured by eddy covariance above a mixed hardwood forest in central Ontario (Haliburton Forest and Wildlife Reserve, or HFWR), and a mixed hardwood forest in northern lower Michigan (Program for Research on Oxidants: Photochemistry, Emissions and Transport, or PROPHET) during the summers of 2011 and 2012 respectively. NO x and NO y mixing ratios were measured by a custom-built two-channel analyser based on chemiluminescence, with selective NO 2 conversion via LED photolysis and NO y conversion via a hot molybdenum converter. Consideration of interferences from water vapour and O 3 , and random uncertainty of the calculated fluxes are discussed. NO y flux observations were predominantly of deposition at both locations. In general, the magnitude of deposition scaled with NO y mixing ratios. Average midday (12:00-16:00) deposition velocities at HFWR and PROPHET were 0.20 ± 0.25 and 0.67 ± 1.24 cm s −1 respectively. Average nighttime (00:00-04:00) deposition velocities were 0.09 ± 0.25 cm s −1 and 0.08 ± 0.16 cm s −1 respectively. At HFWR, a period of highly polluted conditions (NO y concentrations up to 18 ppb) showed distinctly different flux characteristics than the rest of the campaign. Integrated daily average NO y flux was −0.14 mg (N) m −2 day −1 and −0.34 mg (N) m −2 day −1 (net deposition) at HFWR and PROPHET respectively. Concurrent wet deposition measurements were used to estimate the contributions of dry deposition to total reactive nitrogen oxide inputs, found to be 22 and 40 % at HFWR and PROPHET respectively.

Rainfall partitioning through a mixed cedar swamp and associated C and N fluxes in Southern Ontario, Canada

“…Another possible explanation is the crown architecture, with more of the leaf area of T . occidentalis shifted higher in the canopy than the other coniferous species found at the study site (Weiskittel, Kershaw, Hofmeyer, & Seymour, ), thereby intercepting greater amounts of atmospheric dry deposition of nitrogen (Geddes & Murphy, ).…”

A model-based analysis of foliar NO<sub><i>x</i></sub> deposition

“…We do not allow for emission of NO or NO 2 from leaves, consistent with recent laboratory observations that have observed negligible compensation points for these molecules (Chaparro-Suarez et al, 2011;Breuninger et al, 2013;Delaria et al, 2018). All boundary, aerodynamic, cuticular, and soil resistances of O 3 , HNO 3 , CH 2 O, alkyl nitrates (ANs), acyl peroxy nitrates (APNs), HC(O)OH, ROOH, and H 2 O 2 are calculated Geddes and Murphy (2014). b .…”

“…The model was evaluated with comparison to observations from the Biosphere Effects on Aerosols and Photochemistry 2009 (BEARPEX-2009) field campaign from 15 June to 31 July 2009 at Blodgett Forest (Min et al, 2014) and the University of Michigan Biological Station (UMBS) during 5-10 August 2012 (Geddes and Murphy, 2014). For the BEARPEX-2009 calculations, the modeled canopy included an overstory height of 10 m with a one-sided leaf area index of 3.2 m 2 m −2 (LAI os ) and an understory height of 2 m with a LAI of 1.9 m 2 m −2 (LAI us ).…”

“…where k mix = 0.3 h −1 (Wolfe and Thornton, 2011), and C i(adv) is the advection concentration of species i. Advection concentrations are set to fit with the observations during BEARPEX-2009 (Min et al, 2014) or UMBS-2012 (Geddes and Murphy, 2014;Seok et al, 2013) and are used to maintain reasonable background concentrations (Table S1 in the Supplement). Concentrations of NO x , O 3 , and some volatile organic compounds (VOCs) at both sites were influenced by emissions from nearby cities and consequently had sources outside the canopy.…”

Eddy covariance for quantifying trace gas fluxes from soils

“…In the future, COS measurements may lead to a better understanding of both ecosystem carbon cycling and ecosystem sulfur cycling (Kesselmeier et al, 1999;Billesbach et al, 2014). In addition to COS studies that aimed at measuring other compounds such as ozone (O 3 ) and reactive components as part of nitrogen cycling (NO x , which is the sum of NO and NO 2 ; NO y , which is the total of NO x plus additional products of atmospheric oxidation of NO x , namely HNO 3 , HONO, NO 3 , N 2 O 5 , HNO 4 , PAN, RONO 2 , and ROONO 2 ; and ammonia, NH 3 ) with micrometeorological approaches have become available in the past decades (Munger et al, 1996;Eugster and Hesterberg, 1996;Hesterberg et al, 1996;Munger et al, 1998;Famulari et al, 2004;Horii et al, 2004;Jones et al, 2011;Ferrara et al, 2012;Ammann et al, 2012;Marr et al, 2013;Geddes and Murphy, 2014). In particular, the ongoing development of easyto-deploy quantum cascade laser spectrometers capable of measuring various scalars in the field opened the door for fast-response concentration measurements (Bruemmer et al, 2013;Famulari et al, 2004;Skiba et al, 2009;Sutton et al, 2007).…”