Eddy covariance fluxes of peroxyacetyl nitrates (PANs) and NO_y to a coniferous forest

Abstract

[1] We employed a fast response thermal dissociation-chemical ionization mass spectrometer (TD-CIMS) system to measure eddy covariance fluxes of peroxyacetyl nitrate (PAN), peroxypropionyl nitrate (PPN) and peroxymethacryloyl nitrate (MPAN). Average PAN deposition velocities, V d (PAN), showed a daytime maximum of $10.0 mm s À1 ; however, deposition did not cease during nighttime periods. V d (PAN) was highly variable at night and increased when canopy elements were wet from either precipitation or dew formation. Diel patterns of deposition velocity of MPAN and PPN were similar to that of PAN. These results suggest that deposition of PAN, at least to coniferous forest canopies, is much faster than predicted with current deposition algorithms. Although deposition of PAN is unlikely to compete with thermal dissociation during warm summer periods, it will likely play an important role in removing PAN from the atmosphere in colder regions or during winter. The fate of PAN at the surface and within the plants remains unknown, but may present a previously ignored source of nitrogen to ecosystems.

Dry nitrogen deposition estimates over a forest experiencing free air CO2 enrichment

“…It has been suggested that a majority of the dry N flux to most vegetated surfaces is due to HNO 3 vapor although it makes up only 2-10% of the total NO y composition (Williams et al, 1997). However, this study, other measurements made during CELTIC (Turnipseed et al, 2006), and other recent work (Sparks et al, 2003) suggest that peroxynitrates deposit more readily to vegetation than was once thought and can make a significant contribution to the total NO y flux. Given the potential variation in total dry N driven by the compositional differences of NO y outlined above, we have used four scenarios devised to encompass the possible range of NO y -deposition values.…”

“…These tests (conducted upon each calibration) also indicated an adequately fast response (to0.5 s, 1/e). The conversion efficiencies and losses of NO y within our system are discussed more fully in Turnipseed et al (2006). Simply stated, it is likely that there was some loss of HNO 3 within the initial inlet, although the exact amount of loss under the experimental conditions was difficult to quantify.…”

“…Eddy covariance fluxes of NO y A detailed description of the NO y flux measurements and data analysis has been given in Turnipseed et al (2006) and only a brief description will be presented here. Flux measurements were made at a height of 26 m. Three-dimensional wind velocities (u, v, w) were measured at 10 Hz by a sonic anemometer (ATI-K, Advanced Technologies Inc., Boulder, CO, USA).…”

Evaluating the calculated dry deposition velocities of reactive nitrogen oxides and ozone from two community models over a temperate deciduous forest

“…However, a recent field study over a coniferous forest (Turnipseed et al, 2006;Sparks et al, 2008) estimated that HNO 3 accounted for only w24% of the NO y flux and PAN exhibited a close portion of w20%. Zhang et al (2009) investigated the total nitrogen flux budget over eight rural sites across eastern Canada, and estimated that HNO 3 constituted less than half of the NO y flux (46%), and the flux from other measured gaseous nitrogen species (NO 2 þ PAN þ PPN) were also a significant portion (35%).…”

“…Measuring deposition fluxes for reactive nitrogen compounds and O 3 with the eddy-covariance technique (e.g. Munger et al, 1996;Turnipseed et al, 2006) or the gradient method (e.g. Meyers et al, 1989;Sievering et al, 2001) have formed the basis for deposition models aimed at predicting dry depositions of reactive nitrogen compounds and O 3 .…”