scholarly journals Missing peroxy radical sources within a rural forest canopy

2013 ◽  
Vol 13 (12) ◽  
pp. 31713-31759 ◽  
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.

scholarly journals Missing peroxy radical sources within a summertime ponderosa pine forest

2014 ◽  
Vol 14 (9) ◽  
pp. 4715-4732 ◽  
Author(s):  
G. M. Wolfe ◽  
C. Cantrell ◽  
S. Kim ◽  
R. L. Mauldin III ◽  
T. Karl ◽  
...  
Keyword(s):  
Ponderosa Pine ◽  
Forest Canopy ◽  
Strong Dependence ◽  
Rocky Mountain ◽  
Peroxy Radical ◽  
Pine Forest ◽  
Chemical Mechanism ◽  
Peroxy Radicals ◽  
Mixing Ratios ◽  
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.

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

2006 ◽  
Vol 6 (8) ◽  
pp. 2193-2214 ◽  
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.

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

2005 ◽  
Vol 5 (6) ◽  
pp. 12313-12371 ◽  
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.

scholarly journals Comparisons of observed and modeled OH and HO2concentrations during the ambient measurement period of the HOxComp field campaign

2012 ◽  
Vol 12 (5) ◽  
pp. 2567-2585 ◽  
Author(s):  
Y. Kanaya ◽  
A. Hofzumahaus ◽  
H.-P. Dorn ◽  
T. Brauers ◽  
H. Fuchs ◽  
...  
Keyword(s):  
Atmospheric Chemistry ◽  
Chemical Mechanism ◽  
Ozone Production ◽  
High Yield ◽  
Base Case ◽  
Peroxy Radicals ◽  
Field Campaign ◽  
Mixing Ratios ◽  
Measurement Mode ◽  
Single Instrument

Abstract. A photochemical box model constrained by ancillary observations was used to simulate OH and HO2 concentrations for three days of ambient observations during the HOxComp field campaign held in Jülich, Germany in July 2005. Daytime OH levels observed by four instruments were fairly well reproduced to within 33% by a base model run (Regional Atmospheric Chemistry Mechanism with updated isoprene chemistry adapted from Master Chemical Mechanism ver. 3.1) with high R2 values (0.72–0.97) over a range of isoprene (0.3–2 ppb) and NO (0.1–10 ppb) mixing ratios. Daytime HO2(*) levels, reconstructed from the base model results taking into account the sensitivity toward speciated RO2 (organic peroxy) radicals, as recently reported from one of the participating instruments in the HO2 measurement mode, were 93% higher than the observations made by the single instrument. This also indicates an overprediction of the HO2 to OH recycling. Together with the good model-measurement agreement for OH, it implies a missing OH source in the model. Modeled OH and HO2(*) could only be matched to the observations by addition of a strong unknown loss process for HO2(*) that recycles OH at a high yield. Adding to the base model, instead, the recently proposed isomerization mechanism of isoprene peroxy radicals (Peeters and Müller, 2010) increased OH and HO2(*) by 28% and 13% on average. Although these were still only 4% higher than the OH observations made by one of the instruments, larger overestimations (42–70%) occurred with respect to the OH observations made by the other three instruments. The overestimation in OH could be diminished only when reactive alkanes (HC8) were solely introduced to the model to explain the missing fraction of observed OH reactivity. Moreover, the overprediction of HO2(*) became even larger than in the base case. These analyses imply that the rates of the isomerization are not readily supported by the ensemble of radical observations. One of the measurement days was characterized by low isoprene concentrations (∼0.5 ppb) and OH reactivity that was well explained by the observed species, especially before noon. For this selected period, as opposed to the general behavior, the model tended to underestimate HO2(*). We found that this tendency is associated with high NOx concentrations, suggesting that some HO2 production or regeneration processes under high NOx conditions were being overlooked; this might require revision of ozone production regimes.

Incorporation and evaluation of the CRI v2.2 chemical mechanism in UKESM1: An alternative mechanism with updated isoprene chemistry for investigating the influence of BVOCs on atmospheric composition and climate. 

2021 ◽  
Author(s):  
James Weber ◽  
Scott Archer-Nicholls ◽  
N. Luke Abraham ◽  
Youngsub M. Shin ◽  
Thomas Bannan ◽  
...  
Keyword(s):  
Peroxy Radical ◽  
Tropospheric Chemistry ◽  
Chemical Mechanism ◽  
Atmospheric Composition ◽  
Radiation Budget ◽  
Alternative Mechanism ◽  
Mixing Ratios ◽  
The United Kingdom ◽  
Surface Mixing ◽  
Phase Chemistry

<p>We present the first incorporation and evaluation of the Common Representative Intermediates version 2.2 chemistry mechanism, CRI v2.2, for use in the United Kingdom Earth System Model (UKESM1). Tuned against the MCM v3.3.1, the CRI v2.2 mechanism builds on the previous CRI version, CRI v2.1, in UKESM1 (Archer-Nicholls et al., 2020) by updating isoprene chemistry and offers a more comprehensive description of tropospheric chemistry than the standard chemistry mechanism STRAT-TROP (ST).</p><p><span>CRI v2.2 adds state-of-the-art isoprene chemistry with the introduction of HO</span><sub><span>x</span></sub><span>-recycling via the isoprene peroxy radical isomerisation pathway, </span><span>making UKESM1 one of the first CMIP6 models to include this important chemistry. </span><span>HO</span><sub><span>x</span></sub><span>-recycling has noticeable effects on oxidants in regions with large emissions of biogenic volatile organic compounds (BVOCs). Low altitude OH in tropical forested regions increases by 75-150% relative to ST, reducing the existing model low bias compared to observations. Consequently, isoprene surface mixing ratios decrease considerably (25-40%), significantly improving the model high bias relative to ST. Methane lifetime decreases by 2% and tropospheric ozone burden increases by 4%. </span></p><p>Aerosol processes also differ between CRI v2.2 and ST, resulting in changes to the size and number distributions. Relative to ST, CRI v2.2 simulates an 8% decrease in the sulphate aerosol burden with 20% decreases in the nucleation and Aitken modes. By contrast, the secondary organic aerosol (SOA) nucleation mode burden increases by 11%. Globally, the average nucleation and Aitken mode aerosol number concentrations decrease by 20%.</p><p>The differences in aerosol and gas phase chemistry between CRI v2.2 and ST are likely to have impacts on the radiation budget. We plan to use CRI v2.2 and ST to investigate the influence that the chemical mechanism has on the simulated chemistry-climate feedbacks from BVOCs. In addition, CRI v2.2 will serve as the basis for the addition of a scheme describing the formation of highly oxygenated organic molecules (HOMs) from BVOCs, facilitating a semi-explicit mechanism for new particle formation from organic species.</p>

scholarly journals OH and HO<sub>2</sub> radical chemistry in a midlatitude forest: Measurements and model comparisons

2019 ◽  
Author(s):  
Michelle L. Lew ◽  
Pamela S. Rickly ◽  
Brandon P. Bottorff ◽  
Sofia Sklaveniti ◽  
Thierry Léonardis ◽  
...  
Keyword(s):  
Atmospheric Chemistry ◽  
Global Climate ◽  
Oxidation Products ◽  
Chemical Mechanism ◽  
Ozone Production ◽  
Peroxy Radicals ◽  
Mixing Ratios ◽  
Photolysis Rates ◽  
Model Predictions ◽  
Ho2 Radical

Abstract. Reactions of the hydroxyl (OH) and peroxy radicals (HO2 and RO2) play a central role in the chemistry of the atmosphere. In addition to controlling the lifetimes of many trace gases important to issues of global climate change, OH radical reactions initiate the oxidation of volatile organic compounds (VOCs) which can lead to the production of ozone and secondary organic aerosols in the atmosphere. Previous measurements of these radicals in forest environments characterized by high mixing ratios of isoprene and low mixing ratios of nitrogen oxides (NOx) have shown serious discrepancies with modeled concentrations. These results bring into question our understanding of the atmospheric chemistry of isoprene and other biogenic VOCs under low NOx conditions. During the summer of 2015, OH and HO2 radical concentrations as well as total OH reactivity were measured using Laser-Induced Fluorescence - Fluorescence Assay by Gas Expansion (LIF-FAGE) techniques as part of the Indiana Radical, Reactivity and Ozone Production Intercomparison (IRRONIC). This campaign took place in a forested area near the Indiana University, Bloomington campus characterized by high mixing ratios of isoprene and low mixing ratios of NOx. Supporting measurements of photolysis rates, VOCs, NOx, and other species were used to constrain a zero-dimensional box model based on the Regional Atmospheric Chemistry Mechanism (RACM2) and the Master Chemical Mechanism (MCM). Using an OH chemical scavenger technique, the study revealed the presence of an interference with the LIF-FAGE measurements of OH that increased with both ambient concentrations of ozone and temperature. Subtraction of the interference resulted in measured OH concentrations that were in better agreement with model predictions, although the model still underestimated the measured concentrations, likely due to an underestimation of the concentration of NO at this site. Measurements of HO2 radical concentrations during the campaign included a fraction of isoprene-based peroxy radicals (HO2* = HO2 + αRO2) and were found to agree with model predictions. On average, the measured reactivity was consistent with that calculated from measured OH sinks to within 20 %, with modeled oxidation products accounting for the missing reactivity, although significant missing reactivity (approximately 40 % of the total measured reactivity) was observed on some days.

scholarly journals Radicals in the marine boundary layer during NEAQS 2004: a model study of day-time and night-time sources and sinks

2009 ◽  
Vol 9 (9) ◽  
pp. 3075-3093 ◽  
Author(s):  
R. Sommariva ◽  
H. D. Osthoff ◽  
S. S. Brown ◽  
T. S. Bates ◽  
T. Baynard ◽  
...  
Keyword(s):  
Boundary Layer ◽  
New England ◽  
Gas Phase ◽  
Marine Boundary Layer ◽  
Peroxy Radical ◽  
Chemical Mechanism ◽  
Physical Parameters ◽  
Peroxy Radicals ◽  
Night Time ◽  
Aerosol Composition

Abstract. This paper describes a modelling study of several HOx and NOx species (OH, HO2, organic peroxy radicals, NO3 and N2O5) in the marine boundary layer. A model based upon the Master Chemical Mechanism (MCM) was constrained to observations of chemical and physical parameters made onboard the NOAA ship R/V Brown as part of the New England Air Quality Study (NEAQS) in the summer of 2004. The model was used to calculate [OH] and to determine the composition of the peroxy radical pool. Modelled [NO3] and [N2O5] were compared to in-situ measurements by Cavity Ring-Down Spectroscopy. The comparison showed that the model generally overestimated the measurements by 30–50%, on average. The model results were analyzed with respect to several chemical and physical parameters, including uptake of NO3 and N2O5 on fog droplets and on aerosol, dry deposition of NO3 and N2O5, gas-phase hydrolysis of N2O5 and reactions of NO3 with NMHCs and peroxy radicals. The results suggest that fog, when present, is an important sink for N2O5 via rapid heterogeneous uptake. The comparison between the model and the measurements were consistent with values of the heterogeneous uptake coefficient of N2O5 (γN2O5)>1×10−2, independent of aerosol composition in this marine environment. The analysis of the different loss processes of the nitrate radical showed the important role of the organic peroxy radicals, which accounted for a significant fraction (median: 15%) of NO3 gas-phase removal, particularly in the presence of high concentrations of dimethyl sulphide (DMS).

Comparison of Airborne Peroxy Radical Measurements with MECO(n) model simulation during EMeRGe in Europe

2020 ◽  
Author(s):  
Yangzhuoran Liu ◽  
Mariano Mertens ◽  
Maria Dolores Andrés Hernández ◽  
Midhun George ◽  
Vladyslav Nenakhov ◽  
...  
Keyword(s):  
Climate Model ◽  
Model Simulation ◽  
Peroxy Radical ◽  
Photochemical Activity ◽  
Peroxy Radicals ◽  
Transport And Transformation ◽  
Air Masses ◽  
Mixing Ratios ◽  
Airborne Measurement ◽  
On Line

&lt;p&gt;Observations of tropospheric peroxy radicals are a key point for interpretation of the processing and transformation of polluted outflows from major populated centres (MPCs). A series of European MPCs are investigated by the project EMeRGe (Effect of Megacities on the transport and transformation of pollutants on the Regional and Global scales). With this objective two airborne campaigns using the research platform HALO (High Altitude and LOng range aircraft) were carried out over Europe in summer 2017 and over east Asia in the intermonsoon period in 2018. The Institute of Environmental Physics (IUP) in Bremen (Germany) participated in both EMeRGe campaigns with the airborne measurement of the total sum of peroxy radicals, RO&lt;sub&gt;2&lt;/sub&gt;&lt;sup&gt;*&lt;/sup&gt;, by using &amp;#160;the home made PeRCEAS instrument based on the combination of the PERCA (peroxy radical chemical amplification)&amp;#160; and CRDS (cavity ring down spectroscopy) techniques. One of the main purposes of the campaigns was the investigation of the characteristics and chemical transformation of MPC outflows at the local and regional scales.&lt;/p&gt;&lt;p&gt;During the EMeRGe campaign in Europe, air masses of different photochemical activity were measured, where RO&lt;sub&gt;2&lt;/sub&gt;&lt;sup&gt;*&lt;/sup&gt; mixing ratios up to 100pptv being observed. In the present study the RO&lt;sub&gt;2&lt;/sub&gt;&lt;sup&gt;* &lt;/sup&gt;observations for six measurement flights of EMeRGe in Europe have been compared with RO&lt;sub&gt;2&lt;/sub&gt; (here defined as the sum of HO&lt;sub&gt;2 &lt;/sub&gt;+ CH&lt;sub&gt;3&lt;/sub&gt;O&lt;sub&gt;2 &lt;/sub&gt;+ ISOOH + CH&lt;sub&gt;3&lt;/sub&gt;CO&lt;sub&gt;3 &lt;/sub&gt;+ CH&lt;sub&gt;3&lt;/sub&gt;COCH&lt;sub&gt;2&lt;/sub&gt;O&lt;sub&gt;2&lt;/sub&gt;) simulated by using the MECO(n) model.&lt;/p&gt;&lt;p&gt;MECO(n) (MESSy-fied ECHAM and COSMO models nested n times), is &amp;#160;a global/regional chemistry-climate model developed by the MESSy consortium, which couples on-line the global chemistry-climate model EMAC with the regional chemistry-climate model COSMO-CLM/MESSy. The same anthropogenic emission inventory (EDGAR 4.3.1) as well as the same solver for chemical kinetics, involving complex tropospheric and stratospheric chemistry, are applied in EMAC and COSMO-CLM/MESSy.&lt;/p&gt;&lt;p&gt;Overall, the agreement between the measurements and model is reasonable for RO&lt;sub&gt;2&lt;/sub&gt;&lt;sup&gt;* &lt;/sup&gt;observations below 40 pptv. Events with higher mixing ratios seem not to be well reproduced by the model but underestimated. Further details on the modelling and the result of the comparison will be presented.&lt;/p&gt;

scholarly journals Peroxy radical observations over West Africa during the AMMA 2006 campaign: Photochemical activity in episodes of formation of convective systems on the basis of radical measurements

2009 ◽  
Vol 9 (1) ◽  
pp. 1585-1619 ◽  
Author(s):  
M. D. Andrés-Hernández ◽  
D. Kartal ◽  
L. Reichert ◽  
J. P. Burrows ◽  
J. Meyer Arnek ◽  
...  
Keyword(s):  
West Africa ◽  
Biomass Burning ◽  
Peroxy Radical ◽  
Photochemical Activity ◽  
Back Trajectory ◽  
Peroxy Radicals ◽  
Air Masses ◽  
Convective Systems ◽  
Mixing Ratios ◽  
Multidisciplinary Analysis

Abstract. Peroxy radical measurements made on board the DLR-Falcon research aircraft over West Africa within the African Monsoon Multidisciplinary Analysis (AMMA) campaign during the 2006 wet monsoon are presented in this study. The analysis of data focuses on the photochemical activity of air masses sampled during episodes of intense convection and biomass burning. Generally, the total sum of peroxy radical mixing ratios, measured in the outflow of convective clouds, are quite variable but occasionally are coupled with the NO variations indicating the coexistence, or simultaneously emission of NOx, with a potential radical precursor (i.e., formaldehyde, acetone or peroxides) which has likely been transported to higher atmospheric layers. Based on the measurements, significant O3 production rates up to 2 ppb/h in the MCS outflow are estimated by using a box model with simplified chemistry. Peroxy radicals having mixing ratios around 20–25 pptv and with peak values of up to 60–70 pptv are measured within biomass burning plumes, detected at the coast in Ghana. Calculations of back-trajectory densities confirm the origin of these air masses being a biomass burning region at southern latitudes and close to the Gulf of Guinea, according to satellite pictures. Measured peroxy radical concentrations agree reasonably with modelled estimations taking into account simple local chemistry. Moreover the vertical profiles taken at the aircraft base in Ouagadougou, Burkina Faso, indicate the common feature of having maximum concentrations between 2 and 4 km, in agreement with other literature values obtained under similar conditions.

scholarly journals Assessment of the NO-NO<sub>2</sub>-O<sub>3</sub> photostationary state applicability on long-term measurements at the GAW global station Hohenpeissenberg, Germany

2004 ◽  
Vol 4 (2) ◽  
pp. 2003-2036 ◽  
Author(s):  
K. Mannschreck ◽  
S. Gilge ◽  
C. Plass-Duelmer ◽  
W. Fricke ◽  
H. Berresheim
Keyword(s):  
Strong Dependence ◽  
Peroxy Radical ◽  
Strong Impact ◽  
Peroxy Radicals ◽  
Local Effects ◽  
Photostationary State ◽  
Dense Forest ◽  
Meteorological Observatory ◽  
Reactive Gases

Abstract. Continuous measurements of reactive gases, radiation, and meteorological parameters are carried out at the Meteorological Observatory Hohenpeissenberg (MOHp) as part of the Global Atmosphere Watch (GAW) Program. NO, NO2, O3 and JNO2 data from a four year period (March 1999–December 2002) are evaluated for consistency with photochemical steady state (PSS, Φ=1) conditions. In average PSS was reached in 17%, 13%, 22% and 32% of all cases for the year 1999, 2000, 2001 and 2002, respectively. The extent of deviation from PSS reveals a strong dependence on wind direction at the station. Median values of Φ in the south sector are in the range of 2.5–5.7 and show a high variability. In contrast, values for the other directions show a relatively low variability around a median level of 2. These differences can be explained by local effects. It is shown that the height of the sample inlet line, its distance to the forest and the surrounding topography has a strong impact on both the absolute and relative deviations from PSS. Global irradiance and thus, photolysis of NO2 is reduced within the dense forest. Since the reaction of NO with O3 is still proceeding under these conditions, increased NO2/NO ratios are produced locally in air which is transported through the forest and advected to the MOHp site. Estimates of the peroxy radical concentration (RO2) inferred from PSS are compared with peroxy radical measurements made at the site in June 2000 in a three week campaign. The PSS derived RO2 levels were higher than corresponding measured levels by at least a factor of 2–3. This analysis was made for a wind sector with minimal local effects on PSS. Thus the corresponding Φ median of 2 can be regarded as an upper limit for a deviation from PSS due to chemical reactions, i.e. by peroxy radicals and possible other oxidants converting additional NO to NO2.

Sign in / Sign up

Export Citation Format

Share Document