scholarly journals Eddy covariance fluxes and vertical concentration gradient measurements of NO and NO<sub>2</sub> over a ponderosa pine ecosystem: observational evidence for within canopy removal of NO<sub>x</sub>

2013 ◽  
Vol 13 (5) ◽  
pp. 12437-12484 ◽  
Author(s):  
K.-E. Min ◽  
S. E. Pusede ◽  
E. C. Browne ◽  
B. W. LaFranchi ◽  
P. J. Wooldridge ◽  
...  
Keyword(s):  
Ponderosa Pine ◽  
Forest Canopy ◽  
Nutrient Dynamics ◽  
Reduction Factor ◽  
Concentration Gradients ◽  
Free Atmosphere ◽  
Abstract Exchange ◽  
Canopy Removal ◽  
Gradient Measurements ◽  
No Emissions

Abstract. Exchange of NOx (NO+NO2) between the atmosphere and biosphere is important for air quality, climate change, and ecosystem nutrient dynamics. There are few direct ecosystem scale measurements of the direction and rate of atmosphere-biosphere exchange of NOx. As a result, a complete description of the processes affecting NOx following emission from soils and/or plants as they transit from within the plant/forest canopy to the free atmosphere remains poorly constrained and debated. Here, we describe measurements of NO and NO2 fluxes and vertical concentration gradients made during the Biosphere Effects on AeRosols and Photochemistry EXperiment 2009. In general, during daytime we observe upward fluxes of NO and NO2 with counter-gradient fluxes of NO. We find that NOx fluxes from the forest canopy are smaller than calculated using observed flux-gradient relationships for conserved tracers and also smaller than measured soil NO emissions. We interpret these differences as evidence for the existence of a "canopy reduction factor". We suggest that at this site it is primarily due to chemistry converting NOx to higher nitrogen oxides within the forest canopy.

scholarly journals Eddy covariance fluxes and vertical concentration gradient measurements of NO and NO<sub>2</sub> over a ponderosa pine ecosystem: observational evidence for within-canopy chemical removal of NO<sub>x</sub>

2014 ◽  
Vol 14 (11) ◽  
pp. 5495-5512 ◽  
Author(s):  
K.-E. Min ◽  
S. E. Pusede ◽  
E. C. Browne ◽  
B. W. LaFranchi ◽  
R. C. Cohen
Keyword(s):  
Ponderosa Pine ◽  
Large Scale ◽  
Forest Canopy ◽  
Nutrient Dynamics ◽  
Mechanistic Explanation ◽  
Reduction Factor ◽  
Concentration Gradients ◽  
Free Atmosphere ◽  
Abstract Exchange ◽  
Gradient Measurements

Abstract. Exchange of NOx (NO+NO2) between the atmosphere and biosphere is important for air quality, climate change, and ecosystem nutrient dynamics. There are few direct ecosystem-scale measurements of the direction and rate of atmosphere–biosphere exchange of NOx. As a result, a complete description of the processes affecting NOx following emission from soils and/or plants as they transit from within the plant/forest canopy to the free atmosphere remains poorly constrained and debated. Here, we describe measurements of NO and NO2 fluxes and vertical concentration gradients made during the Biosphere Effects on AeRosols and Photochemistry EXperiment 2009. In general, during daytime we observe upward fluxes of NO and NO2 with counter-gradient fluxes of NO. We find that NOx fluxes from the forest canopy are smaller than calculated using observed flux–gradient relationships for conserved tracers and also smaller than measured soil NO emissions. We interpret these differences as primarily due to chemistry converting NOx to higher nitrogen oxides within the forest canopy, which might be part of a mechanistic explanation for the "canopy reduction factor" applied to soil NOx emissions in large-scale models.

Time- and pH-dependent leaching of ions from deciduous and coniferous foliage

1990 ◽  
Vol 20 (11) ◽  
pp. 1779-1785 ◽  
Author(s):  
L. J. Puckett
Keyword(s):  
Ion Exchange ◽  
Anion Exchange ◽  
Forest Canopy ◽  
Ion Selectivity ◽  
White Pine ◽  
Natural Conditions ◽  
Canopy Removal ◽  
Exchange Medium ◽  
Experiment Duration

Leaching of ions from foliage of black gum (Nyssasylvatica Marsh.), chestnut oak (Quercusprinus L.), and white pine (Pinusstrobus L.) in response to increasing exposure time to and concentration of H+ was examined in a laboratory study. Ten individual leaves and needle bundles were exposed to H+ solutions at pH 3.0, 4.0, and 5.6 for periods of 5, 50, 500, and 1000 min. Increases in the removal of Ca2+ and Mg2+ from all species tested were strongly related to increases in experiment duration and H+ concentration, confirming the role of ion exchange in the removal of these ions from the forest canopy. Removal of Na+ and K+ did not appear to be strongly influenced by ion exchange. Positive relations between SO42− and H+ (and presumably Cl−) for the deciduous species suggest that anion exchange may be involved in the removal process. Given the relatively small number of anion exchange sites on cuticles, and because SO42− is the primary anion in both rain and throughfall, anion exchange is not likely to contribute significant amounts of anions under natural conditions. It is difficult to extrapolate results from an experiment of this type to what might be expected under natural conditions. However, the response of whole leaves and needles fits that expected based on the ion selectivity of the cuticle as a carboxylic acid ion-exchange medium and holds promise for understanding the processes involved in ion leaching from forest canopies.

scholarly journals Uptake and emission of VOCs near ground level below a mixed forest at Borden, Ontario

2014 ◽  
Vol 14 (4) ◽  
pp. 4505-4535
Author(s):  
M. Gordon ◽  
A. Vlasenko ◽  
R. M. Staebler ◽  
C. Stroud ◽  
P. A. Makar ◽  
...  
Keyword(s):  
Forest Canopy ◽  
Mixed Forest ◽  
Ground Level ◽  
Proton Transfer Reaction ◽  
Emission Rates ◽  
Concentration Gradients ◽  
Surface Deposition ◽  
Canopy Exchange ◽  
Surface Emission ◽  
Deposition Velocities

Abstract. Understanding of the atmosphere/forest canopy exchange of volatile organic compounds (VOCs) requires insight into deposition, emission, and chemical reactions of VOCs below the canopy. Currently, uncertainties in canopy processes, such as stomatal uptake, deposition, and sub-canopy chemistry, make it difficult to derive biogenic VOC emission inventories from canopy VOC concentration gradients. Between 18 July and 9 August 2009, VOCs were measured with proton-transfer-reaction mass spectrometry (PTR-MS) at 6 heights between 1 and 6 m beneath a 23 m high mixed-forest canopy. Measured VOCs included methanol, isoprene, acetone, methacrolein + methyl vinyl ketone (MACR+MVK), monoterpenes and sesquiterpenes. There are pronounced differences in the behaviour of isoprene and its by-products and that of the terpenes. Non-terpene fluxes are predominantly downward. In contrast, the terpene fluxes are significantly upward. A 1-dimensional canopy model was used to compare results to measurements with and without surface deposition of isoprene and MACR+MVK and emissions of monoterpenes and sesquiterpenes. Results suggest deposition velocities of 27 mm s−1 for isoprene and 12 mm s−1 for MACR+MVK and daytime surface emission rates of 63 μg m−2 h−1 for monoterpenes. The modelled isoprene surface deposition is approximately 2% of the canopy top isoprene emissions and the modelled emissions of monoterpenes comprise approximately 15 to 27% of the canopy-top monoterpene emissions to the atmosphere. These results suggest that surface monoterpene emissions are significant for forest canopy/atmosphere exchange for this mixed forest location and surface uptake is relatively small for all the species measured in this study.

scholarly journals Observations of HNO<sub>3</sub>, ΣAN, ΣPN and NO<sub>2</sub> fluxes: evidence for rapid HO<sub>x</sub> chemistry within a pine forest canopy

2007 ◽  
Vol 7 (3) ◽  
pp. 7087-7136 ◽  
Author(s):  
D. K. Farmer ◽  
R. C. Cohen
Keyword(s):  
Nitrogen Oxides ◽  
Sierra Nevada ◽  
Residence Time ◽  
Ponderosa Pine ◽  
Forest Canopy ◽  
Similarity Theory ◽  
Peroxy Radical ◽  
Pine Forest ◽  
Alkyl Nitrates ◽  
Emission Fluxes

Abstract. Measurements of exchange of reactive nitrogen oxides between the atmosphere and a ponderosa pine forest in the Sierra Nevada Mountains are reported. During winter, we observe upward fluxes of NO2, and downward fluxes of total peroxy and peroxy acyl nitrates (ΣPNs), total gas and particle phase alkyl and multifunctional alkyl nitrates (ΣANs(g+p), and the sum of gaseous HNO3 and semi-volatile NO3− particles (HNO3(g+p). We use calculations of the vertical profile and flux of NO, partially constrained by observations, to show that net midday ΣNOyi fluxes in winter are –4.9 ppt m s−1. The signs and magnitudes of these wintertime individual and ΣNOyi fluxes are in the range of prior measurements. In contrast, during summer, we observe downward fluxes only of ΣANs(g+p), and upward fluxes of HNO3(g+p), ΣPNs and NO2 with signs and magnitudes that are unlike most, if not all, previous observations and analyses of fluxes of individual nitrogen oxides. The results imply that the mechanisms contributing to NOy fluxes, at least at this site, are much more complex than previously recognized. We show that the observations of upward fluxes of HNO3(g+p) and ΣPNs during summer are consistent with oxidation of NO2 and acetaldehyde by OH with the product of concentration and residence time equal to 1.1×1010 molec OH cm−3 s, e.g. 3×107 molecules cm−3 OH for a 400 s canopy residence time. We show that ΣAN(g+p) fluxes are consistent with this same OH if the reaction of OH with ΣANs produces either HNO3 or NO2 in 6–30% yield. Calculations of NO fluxes constrained by the NO2 observations and the inferred OH indicate that NOx fluxes are downward into the canopy because of the substantial conversion of NOx to HNO3 and ΣPNs in the canopy. Even so, we derive that NOx emission fluxes of ~15 ng(N) m−2 s−1 at midday during summer are required to balance the NOx and NOy flux budgets. These fluxes are partly explained by estimates of soil emissions (estimated to be between 3 and 6 ng(N) m−2 s−1). One possibility for the remainder of the NOx source is large HONO emissions. Alternatively, the 15 ng(N) m−2 s−1 emission estimate may be too large, and the budget balanced if the deposition of HNO3 and ΣPNs is slower than we estimate, if there are large errors in either our understanding of peroxy radical chemistry, or our assumptions that the budget is required to balance because the fluxes do not obey similarity theory.

scholarly journals Observations of atmosphere-biosphere exchange of total and speciated peroxynitrates: nitrogen fluxes and biogenic sources of peroxynitrates

2012 ◽  
Vol 12 (2) ◽  
pp. 6205-6233 ◽  
Author(s):  
K.-E. Min ◽  
S. E. Pusede ◽  
E. C. Browne ◽  
B. W. LaFranchi ◽  
P. J. Wooldridge ◽  
...  
Keyword(s):  
Ponderosa Pine ◽  
Global Scale ◽  
Time Of Day ◽  
Concentration Gradients ◽  
Nitrogen Fluxes ◽  
Plant Canopies ◽  
Biogenic Voc ◽  
The Impact ◽  
Ponderosa Pine Forest ◽  
Recent Laboratory

Abstract. Peroxynitrates are responsible for global scale transport of reactive nitrogen. Recent laboratory observations suggest that they may also play an important role in delivery of nutrients to plant canopies. We measured eddy covariance fluxes of total peroxynitrates (ΣPNs) and three individual peroxynitrates (APNs ≡ PAN + PPN + MPAN) over a ponderosa pine forest during the Biosphere Effects on AeRosols and Photochemistry EXperiment 2009 (BEARPEX 2009). Concentrations of these species were also measured at multiple heights above and within the canopy. While the above-canopy daytime concentrations are nearly identical for ΣPNs and APNs, we observed the downward flux of ΣPNs to be 30–60% slower than the flux of APNs. The vertical concentration gradients of ΣPNs and APNs vary with time of day and exhibit different temperature dependencies. These differences can be explained by the production of peroxynitrates other than PAN, PPN, and MPAN within the canopy (presumably as a consequence of biogenic VOC emissions) and upward fluxes of these PN species. The impact of this implied peroxynitrate flux on the interpretation of NOx fluxes and ecosystem N exchange is discussed.

scholarly journals In-situ ambient quantification of monoterpenes, sesquiterpenes, and related oxygenated compounds during BEARPEX 2007: implications for gas- and particle-phase chemistry

2009 ◽  
Vol 9 (15) ◽  
pp. 5505-5518 ◽  
Author(s):  
N. C. Bouvier-Brown ◽  
A. H. Goldstein ◽  
J. B. Gilman ◽  
W. C. Kuster ◽  
J. A. de Gouw
Keyword(s):  
Sierra Nevada ◽  
Atmospheric Chemistry ◽  
Ponderosa Pine ◽  
Forest Canopy ◽  
Loss Rate ◽  
Weather Conditions ◽  
Particle Phase ◽  
Aerosol Mass ◽  
Phase Chemistry

Abstract. We quantified ambient mixing ratios of 9 monoterpenes, 6 sesquiterpenes, methyl chavicol, the oxygenated terpene linalool, and nopinone using an in-situ gas chromatograph with a quadrupole mass spectrometer (GC-MS). These measurements were a part of the 2007 Biosphere Effects on AeRosols and Photochemistry EXperiment (BEARPEX) at Blodgett Forest, a ponderosa pine forest in the Sierra Nevada Mountains of California. To our knowledge, these observations represent the first direct in-situ ambient quantification of the sesquiterpenes α-bergamotene, longifolene, α-farnesene, and β-farnesene. From average diurnal mixing ratio profiles, we show that α-farnesene emissions are dependent mainly on temperature whereas α-bergamotene and β-farnesene emissions are temperature- and light-dependent. The amount of sesquiterpene mass quantified above the canopy was small (averaging a total of 3.3 ppt during the day), but nevertheless these compounds contributed 7.6% to the overall ozone-olefin loss rate above the canopy. Assuming that the monoterpene-to-sesquiterpene emission rate in the canopy is similar to that observed in branch enclosure studies at the site during comparable weather conditions, and the average yield of aerosol mass from these sesquiterpenes is 10–50%, the amount of sesquiterpene mass reacted within the Blodgett Forest canopy alone accounts for 6–32% of the total organic aerosol mass measured during BEARPEX. The oxygenated monoterpene linalool was also quantified for the first time at Blodgett Forest. The linalool mass contribution was small (9.9 ppt and 0.74 ppt within and above the canopy, respectively), but it contributed 1.1% to the total ozone-olefin loss rate above the canopy. Reactive and semi-volatile compounds, especially sesquiterpenes, significantly impact the gas- and particle-phase chemistry of the atmosphere at Blodgett Forest and should be included in both biogenic volatile organic carbon emission and atmospheric chemistry models.

Assessing the atmosphere-surface exchange of gaseous elemental mercury using passive air samplers

2020 ◽  
Author(s):  
Meng Si ◽  
Michelle Feigis ◽  
Isabel Quant ◽  
Shreya Mistry ◽  
Melanie Snow ◽  
...  
Keyword(s):  
Time Scales ◽  
Forest Canopy ◽  
Elemental Mercury ◽  
Permafrost Degradation ◽  
Concentration Gradients ◽  
Surface Exchange ◽  
Gaseous Elemental Mercury ◽  
The Earth ◽  
Long Time ◽  
The Impact

&lt;p&gt;The specific properties of gaseous elemental mercury (GEM) allow it to undergo bidirectional exchange between the atmosphere and the Earth&amp;#8217;s surface. Determining the direction and the magnitude of GEM&amp;#8217;s atmosphere-surface flux is possible and has been accomplished using micrometeorological and chamber techniques, but (i) is complex and labor-intensive, and (ii) often only yields fluxes over relatively short time scales. A recently developed passive air sampler for GEM has the precision required for identifying and quantifying vertical concentration gradients above the Earth&amp;#8217;s surface. The feasibility and performance of this approach is currently being tested in a number of field studies aimed at the: (i) measurement of GEM concentration gradients above both mercury-contaminated and background forest soils, (ii) quantification of vertical concentration gradients on a tower through a temperate deciduous forest canopy, and (iii) measurement of mercury concentration gradients over stable and thawing permafrost to determine the effect of permafrost degradation on GEM evasion. Contrasting with earlier flux studies, these investigations cover long time periods (up to 1.5 years) and have coarse temporal resolution (monthly to seasonally). Significant gradients of GEM air concentrations, both increasing and decreasing with height above ground, were observed, implying that at a minimum, the method is able to identify the flux direction of GEM. Under the right circumstances, this method can also be used to estimate the approximate magnitude of the GEM air-surface exchange flux. The measured gradients also reveal the impact of factors such as temperature, solar irradiance, and snow cover on air-surface exchange. The method holds promise for establishing the direction and size of exchange fluxes at long time scales of months to a year, especially in study areas where access, effort and cost are prohibitive to longer duration studies with existing approaches.&lt;/p&gt;

scholarly journals Observations of atmosphere-biosphere exchange of total and speciated peroxynitrates: nitrogen fluxes and biogenic sources of peroxynitrates

2012 ◽  
Vol 12 (20) ◽  
pp. 9763-9773 ◽  
Author(s):  
K.-E. Min ◽  
S. E. Pusede ◽  
E. C. Browne ◽  
B. W. LaFranchi ◽  
P. J. Wooldridge ◽  
...  
Keyword(s):  
Ponderosa Pine ◽  
Global Scale ◽  
Time Of Day ◽  
Concentration Gradients ◽  
Nitrogen Fluxes ◽  
Plant Canopies ◽  
Biogenic Voc ◽  
The Impact ◽  
Ponderosa Pine Forest ◽  
Recent Laboratory

Abstract. Peroxynitrates are responsible for global scale transport of reactive nitrogen. Recent laboratory observations suggest that they may also play an important role in delivery of nutrients to plant canopies. We measured eddy covariance fluxes of total peroxynitrates (ΣPNs) and three individual peroxynitrates (APNs ≡ PAN + PPN + MPAN) over a ponderosa pine forest during the Biosphere Effects on AeRosols and Photochemistry EXperiment 2009 (BEARPEX 2009). Concentrations of these species were also measured at multiple heights above and within the canopy. While the above-canopy daytime concentrations are nearly identical for ΣPNs and APNs, we observed the downward flux of ΣPNs to be 30–60% slower than the flux of APNs. The vertical concentration gradients of ΣPNs and APNs vary with time of day and exhibit different temperature dependencies. These differences can be explained by the production of peroxynitrates other than PAN, PPN, and MPAN within the canopy (presumably as a consequence of biogenic VOC emissions) and upward fluxes of these PN species. The impact of this implied peroxynitrate flux on the interpretation of NOx fluxes and ecosystem N exchange is discussed.

Decomposition and nutrient dynamics of ponderosa pine needles in a Mediterranean-type climate

1992 ◽  
Vol 22 (3) ◽  
pp. 306-314 ◽  
Author(s):  
Stephen C. Hart ◽  
Mary K. Firestone ◽  
Eldor A. Paul
Keyword(s):  
Sierra Nevada ◽  
Ponderosa Pine ◽  
Nutrient Dynamics ◽  
Decay Rates ◽  
Litter Fall ◽  
Decomposition Rates ◽  
Old Growth ◽  
Old Growth Forest ◽  
Significant Difference ◽  
Young Growth

A litter-bag technique was used to measure decay rates and assess changes in organic and inorganic constituents of ponderosa pine (Pinusponderosa Laws.) needle litter during decomposition over a 2-year period in old- and young-growth forests in the Sierra Nevada of California. Rates of mass loss were among the lowest reported for temperate and boreal forests, with annual decomposition constants of about 0.08 and 0.18 year−1 for the old- and young-growth forests, respectively. Apparently, the temporal separation of warm temperatures and moist conditions found in Mediterranean-type climates severely limits decomposition in these coniferous forests. In the old-growth forest, comparison of estimates of tree nutrient uptake with net releases of nutrients from fine litter during their 1st year of decomposition suggests that recent litter fall potentially acts as a significant source of P, Mg, and K for tree uptake in this forest; in contrast, recently fallen litter acts as a net sink for N, S, and Ca. Despite initially lower indices of litter quality for litter originating from the old–growth relative to the young–growth forest, no significant difference in decomposition rates of these two litter age-classes was found when placed at either site. This result does not support the hypothesis that decreases in decomposition rates during forest development are driven by decreases in the quality of litter fall.

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