Missing peroxy radical sources within a summertime ponderosa pine forest

Abstract. Organic peroxy (RO2) and hydroperoxy (HO2) radicals are key intermediates in the photochemical processes that generate ozone, secondary organic aerosol and reactive nitrogen reservoirs throughout the troposphere. In regions with ample biogenic hydrocarbons, the richness and complexity of peroxy radical chemistry presents a significant challenge to current-generation models, especially given the scarcity of measurements in such environments. We present peroxy radical observations acquired within a ponderosa pine forest during the summer 2010 Bio-hydro-atmosphere interactions of Energy, Aerosols, Carbon, H2O, Organics and Nitrogen – Rocky Mountain Organic Carbon Study (BEACHON-ROCS). Total peroxy radical mixing ratios reach as high as 180 pptv (parts per trillion by volume) and are among the highest yet recorded. Using the comprehensive measurement suite to constrain a near-explicit 0-D box model, we investigate the sources, sinks and distribution of peroxy radicals below the forest canopy. The base chemical mechanism underestimates total peroxy radicals by as much as a factor of 3. Since primary reaction partners for peroxy radicals are either measured (NO) or underpredicted (HO2 and RO2, i.e., self-reaction), missing sources are the most likely explanation for this result. A close comparison of model output with observations reveals at least two distinct source signatures. The first missing source, characterized by a sharp midday maximum and a strong dependence on solar radiation, is consistent with photolytic production of HO2. The diel profile of the second missing source peaks in the afternoon and suggests a process that generates RO2 independently of sun-driven photochemistry, such as ozonolysis of reactive hydrocarbons. The maximum magnitudes of these missing sources (~120 and 50 pptv min−1, respectively) are consistent with previous observations alluding to unexpectedly intense oxidation within forests. We conclude that a similar mechanism may underlie many such observations.

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Missing peroxy radical sources within a rural forest canopy

Atmospheric Chemistry and Physics Discussions ◽

10.5194/acpd-13-31713-2013 ◽

2013 ◽

Vol 13 (12) ◽

pp. 31713-31759 ◽

Cited By ~ 1

Author(s):

G. M. Wolfe ◽

C. Cantrell ◽

S. Kim ◽

R. L. Mauldin ◽

T. Karl ◽

...

Keyword(s):

Ponderosa Pine ◽

Forest Canopy ◽

Strong Dependence ◽

Rocky Mountain ◽

Peroxy Radical ◽

Chemical Mechanism ◽

Peroxy Radicals ◽

Mixing Ratios ◽

Distinct Source ◽

Measurement Suite

Abstract. Organic peroxy (RO2) and hydroperoxy (HO2) radicals are key intermediates in the photochemical processes that generate ozone, secondary organic aerosol and reactive nitrogen reservoirs throughout the troposphere. In regions with ample biogenic hydrocarbons, the richness and complexity of peroxy radical chemistry presents a significant challenge to current-generation models, especially given the scarcity of measurements in such environments. We present peroxy radical observations acquired within a Ponderosa pine forest during the summer 2010 Bio-hydro-atmosphere interactions of Energy, Aerosols, Carbon, H2O, Organics and Nitrogen – Rocky Mountain Organic Carbon Study (BEACHON-ROCS). Total peroxy radical mixing ratios reach as high as 180 pptv and are among the highest yet recorded. Using the comprehensive measurement suite to constrain a near-explicit 0-D box model, we investigate the sources, sinks and distribution of peroxy radicals below the forest canopy. The base chemical mechanism underestimates total peroxy radicals by as much as a factor of 3. Since primary reaction partners for peroxy radicals are either measured (NO) or under-predicted (HO2 and RO2, i.e. self-reaction), missing sources are the most likely explanation for this result. A close comparison of model output with observations reveals at least two distinct source signatures. The first missing source, characterized by a sharp midday maximum and a strong dependence on solar radiation, is consistent with photolytic production of HO2. The diel profile of the second missing source peaks in the afternoon and suggests a process that generates RO2 independently of sun-driven photochemistry, such as ozonolysis of reactive hydrocarbons. The maximum magnitudes of these missing sources (~ 120 and 50 pptv min−1, respectively) are consistent with previous observations alluding to unexpectedly intense oxidation within forests. We conclude that a similar mechanism may underlie many such observations.

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Peroxy radical chemistry and the control of ozone photochemistry at Mace Head, Ireland during the summer of 2002

Atmospheric Chemistry and Physics ◽

10.5194/acp-6-2193-2006 ◽

2006 ◽

Vol 6 (8) ◽

pp. 2193-2214 ◽

Cited By ~ 59

Author(s):

Z. L. Fleming ◽

P. S. Monks ◽

A. R. Rickard ◽

D. E. Heard ◽

W. J. Bloss ◽

...

Keyword(s):

Boundary Layer ◽

Production Rate ◽

Marine Boundary Layer ◽

Strong Dependence ◽

Peroxy Radical ◽

Chemical Mechanism ◽

Ozone Production ◽

Peroxy Radicals ◽

Night Time ◽

Model Measurement

Abstract. Peroxy radical (HO2+ΣRO2) measurements, using the PEroxy Radical Chemical Amplification (PERCA) technique at the North Atlantic Marine Boundary Layer EXperiment (NAMBLEX) at Mace Head in summer 2002, are presented and put into the context of marine, boundary-layer chemistry. A suite of other chemical parameters (NO, NO2, NO3, CO, CH4, O3, VOCs, peroxides), photolysis frequencies and meteorological measurements, are used to present a detailed analysis of the role of peroxy radicals in tropospheric oxidation cycles and ozone formation. Under the range of conditions encountered the peroxy radical daily maxima varied from 10 to 40 pptv. The diurnal cycles showed an asymmetric shape typically shifted to the afternoon. Using a box model based on the master chemical mechanism the average model measurement agreement was 2.5 across the campaign. The addition of halogen oxides to the model increases the level of model/measurement agreement, apparently by respeciation of HOx. A good correlation exists between j(HCHO).[HCHO] and the peroxy radicals indicative of the importance of HCHO in the remote atmosphere as a HOx source, particularly in the afternoon. The peroxy radicals showed a strong dependence on [NO2] with a break point at 0.1 ppbv, where the radicals increased concomitantly with the reactive VOC loading, this is a lower value than seen at representative urban campaigns. The HO2/(HO2+ΣRO2) ratios are dependent on [NOx] ranging between 0.2 and 0.6, with the ratio increasing linearly with NOx. Significant night-time levels of peroxy radicals were measured up to 25 pptv. The contribution of ozone-alkenes and NO3-alkene chemistry to night-time peroxy radical production was shown to be on average 59 and 41%. The campaign mean net ozone production rate was 0.11±0.3 ppbv h-1. The ozone production rate was strongly dependent on [NO] having linear sensitivity (dln(P(O3))/dln(NO)=1.0). The results imply that the N(O3) (the in-situ net photochemical rate of ozone production/destruction) will be strongly sensitive in the marine boundary layer to small changes in [NO] which has ramifications for changing NOx loadings in the European continental boundary layer.

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Observations of HNO3, ΣAN, ΣPN and NO2 fluxes: evidence for rapid HOx chemistry within a pine forest canopy

Atmospheric Chemistry and Physics Discussions ◽

10.5194/acpd-7-7087-2007 ◽

2007 ◽

Vol 7 (3) ◽

pp. 7087-7136 ◽

Cited By ~ 5

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.

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Peroxy radical chemistry and the control of ozone photochemistry at Mace Head, Ireland during the summer of 2002

Atmospheric Chemistry and Physics Discussions ◽

10.5194/acpd-5-12313-2005 ◽

2005 ◽

Vol 5 (6) ◽

pp. 12313-12371 ◽

Cited By ~ 4

Author(s):

Z. L. Fleming ◽

P. S. Monks ◽

A. R. Rickard ◽

D. E. Heard ◽

W. J. Bloss ◽

...

Keyword(s):

Boundary Layer ◽

Production Rate ◽

Marine Boundary Layer ◽

Strong Dependence ◽

Peroxy Radical ◽

Chemical Mechanism ◽

Ozone Production ◽

Peroxy Radicals ◽

Night Time ◽

Model Measurement

Abstract. Peroxy radical (HO2+ΣRO2) measurements, using the PEroxy Radical Chemical Amplification (PERCA) technique at the North Atlantic Marine Boundary Layer EXperiment (NAMBLEX) at Mace Head in summer 2002, are presented and put into the context of marine, boundary-layer chemistry. A suite of other chemical parameters (NO, NO2, NO3, CO, CH4, O3, VOCs, peroxides), photolysis frequencies and meteorological measurements, are used to present a detailed analysis of the role of peroxy radicals in tropospheric oxidation cycles and ozone formation. Under the range of conditions encountered the peroxy radical daily maxima varied from 10 to 40 pptv. The diurnal cycles showed an asymmetric shape typically shifted to the afternoon. Using a box model based on the master chemical mechanism the average model measurement agreement was 2.5 across the campaign. The addition of halogen oxides to the model increases the level of model/measurement agreement, apparently by respeciation of HOx. A good correlation exists between j(HCHO).[HCHO] and the peroxy radicals indicative of the importance of HCHO in the remote atmosphere as a HOx source, particularly in the afternoon. The peroxy radicals showed a strong dependence on [NOx] with a break point at 0.1 ppbv, where the radicals increased concomitantly with the reactive VOC loading, this is a lower value than seen at representative urban campaigns. The HO2/(HO2+ΣRO2) ratios are dependent on [NOx] ranging between 0.2 and 0.6, with the ratio increasing linearly with NOx. Significant night-time levels of peroxy radicals were measured up to 25 pptv. The contribution of ozone-alkenes and NO3-alkene chemistry to night-time peroxy radical production was shown to be on average 59 and 41%. The campaign mean net ozone production rate was 0.11±0.3 ppbv h−1. The ozone production rate was strongly dependent on [NO] having linear sensitivity (dln(P(O3))/dln(NO)=1.0). The results imply that the N(O3) (the in-situ net photochemical rate of ozone production/destruction) will be strongly sensitive in the marine boundary layer to small changes in [NO] which has ramifications for changing NOx loadings in the European continental boundary layer.

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Observations of HNO3, ΣAN, ΣPN and NO2 fluxes: evidence for rapid HOx chemistry within a pine forest canopy

Atmospheric Chemistry and Physics ◽

10.5194/acp-8-3899-2008 ◽

2008 ◽

Vol 8 (14) ◽

pp. 3899-3917 ◽

Cited By ~ 78

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 an OH x residence time of 1.1×1010 molec OH cm−3 s, corresponding to 3 to 16×107 molecules cm−3 OH within the forest canopy for a 420 to 70 s canopy residence time. We show that ΣAN(g+p) fluxes are consistent with this range in OH if the reaction of OH with ΣANs produces either HNO3 or NO2 with a 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.

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Observations of oxidation products above a forest imply biogenic emissions of very reactive compounds

Atmospheric Chemistry and Physics ◽

10.5194/acp-5-67-2005 ◽

2005 ◽

Vol 5 (1) ◽

pp. 67-75 ◽

Cited By ~ 188

Author(s):

R. Holzinger ◽

A. Lee ◽

K. T. Paw ◽

U. A. H. Goldstein

Keyword(s):

Ponderosa Pine ◽

Forest Canopy ◽

Large Fraction ◽

Oxidation Products ◽

Biogenic Emissions ◽

Central California ◽

Mixing Ratios ◽

Volatile Organic ◽

Current Emission ◽

Ponderosa Pine Forest

Abstract. Vertical gradients of mixing ratios of volatile organic compounds have been measured in a Ponderosa pine forest in Central California (38.90° N, 120.63° W, 1315m). These measurements reveal large quantities of previously unreported oxidation products of short lived biogenic precursors. The emission of biogenic precursors must be in the range of 13-66µmol m-2h-1 to produce the observed oxidation products. That is 6-30 times the emissions of total monoterpenes observed above the forest canopy on a molar basis. These reactive precursors constitute a large fraction of biogenic emissions at this site, and are not included in current emission inventories. When oxidized by ozone they should efficiently produce secondary aerosol and hydroxyl radicals.

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