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1.
Accurate OH and HO2 (collectively called HOx) measurements by laser-induced fluorescence (LIF) may be contaminated by spurious signals from interfering atmospheric chemicals or from the instrument itself. Interference tests must be conducted to ensure that observed OH signal originates solely from ambient OH and is not due to instrument artifacts. Several tests were performed on the Penn State LIF HOx instrument, both in the laboratory and in the field. Theseincluded measurements of the instrument's zero signal by using either zero air or perfluoropropylene to remove OH, examination of spectral interferences from naphthalene, sulfur dioxide, and formaldehyde, and tests of interferences by addition of suspected interfering atmospheric chemicals, including ozone, hydrogen peroxide, nitrous acid, formaldehyde, nitric acid, acetone, and organic peroxy radicals (RO2). All tests lacked evidence ofsignificant interferences for measurements in the atmosphere, including highly polluted urban environments.  相似文献   

2.
Simultaneous measurements of ozone and ozoneprecursors were made during a field campaign atSchauinsland in the Black Forest and in the valleynorth of Schauinsland that channels the flow ofpolluted air from the city of Freiburg to the site.From the decay of hydrocarbons and NOx between the twomeasuring sites and the known rate coefficients, theconcentration of OH radicals was calculated. From abudget analysis of OH and HOx it is concluded that therelatively high OH concentrations (5–8 ×106cm-3) in the presence of high NO2concentrations cannot be explained by the knownprimary sources. The budget can be closed if efficientrecycling of OH via HO2 is assumed to occur andthat, based on the measured hydrocarbons, 2 HO2molecules are formed for each OH radical that reactswith a hydrocarbon molecule. This assumption is inaccordance with the budget of Ox obtained from ourmeasurements and with results from earliermeasurements of alkylnitrates and peroxy radicals atSchauinsland. A possible conclusion is that the decayof precursors and production of photooxidants in urbanplumes proceeds at a faster rate than is currentlyassumed. The potential role of biogenichydrocarbons for the radical budget is alsodiscussed.  相似文献   

3.
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4.
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5.
Atmospheric hydroxyl (OH), hydroperoxy (HO2), total peroxy (HO2 and organic peroxy radicals, RO2) mixing ratios and OH reactivity (first order OH loss rate) were measured at a rural site in central Pennsylvania during May and June 2002. OH and HO2 mixing ratios were measured with laser induced fluorescence (LIF); HO2 + RO2 mixing ratios were measured with chemical ionization mass spectrometry (CIMS). The daytime maximum mixing ratios were up to 0.6 parts per trillion by volume (pptv) for OH, 30 pptv for HO2, and 45 pptv for HO2 + RO2. A parameterized RACM (Regional Atmospheric Chemistry Mechanism) box model was used to predict steady state OH, HO2 and HO2 + RO2 concentrations by constraining the model to the measured OH reactivity and previously measured volatile organic compound (VOC) distributions. The averaged model calculations are generally in good agreement with the observations. For OH, the model matched the observations for day and night, with an average observed-to-modeled ratio of 0.80. In previous studies such as PROPHET98, nighttime NO was near 0 pptv and observed nighttime OH was significantly larger than modeled OH. In this study, nighttime observed and modeled OH agree to within measurement and model uncertainties because the main source of the nighttime OH was the reaction HO2 + NO → OH + NO2, with the NO being continually emitted from the surrounding fertilized corn field. The observed-to-modeled ratio for HO2 is 1.0 on average, although daytime HO2 is underpredicted by a factor of 1.2 and nighttime HO2 is over-predicted by a factor of ∼2. The average measured and modeled HO2 + RO2 agree well during daytime, but the modeled value is about twice the measured value during nighttime. While measured HO2 + RO2 values agree with modeled values for NO mixing ratios less than a few parts per billion by volume (ppbv), it increases substantially above the expected value for NO greater than a few ppbv. This observation of the higher-than-expected HO2 + RO2 with the CIMS technique confirms the observed increase of HO2 above expected values at higher NO mixing ratios in HO2 measurements with the LIF technique. The maximum instantaneous O3 production rate calculated from HO2 and RO2 reactions with NO was as high as 10–15 ppb h−1 at midday; the total daily O3 production varied from 13 to 113 ppbv d−1 and was 48 ppbv d−1 on average during this campaign.  相似文献   

6.
Simultaneous measurements of peroxy and nitrate radicals at Schauinsland   总被引：3，自引：0，他引：3  
We present simultaneous field measurements of NO3 and peroxy radicals made at night in a forested area (Schauinsland, Black Forest, 48° N, 8° N, 1150 ASL), together with measurements of CO, O3, NO x , NO y , and hydrocarbons, as well as meteorological parameters. NO2, NO3, HO2, and (RO2) radicals are detected with matrix isolation/electron spin resonance (MIESR). NO3 and HO2 were found to be present in the range of 0–10 ppt, whilst organic peroxy radicals reached concentrations of 40 ppt. NO3, RO2, and HO2 exhibited strong variations, in contrast to the almost constant values of the longer lived trace gases. The data suggest anticorrelation between NO3 and RO2 radical concentrations at night.The measured trace gas set allows the calculation of NO3 and peroxy radical concentrations, using a chemical box model. From these simulations, it is concluded that the observed anthropogenic hydrocarbons are not sufficient to explain the observed RO2 concentrations. The chemical budget of both NO3 and RO2 radicals can be understood if emissions of monoterpenes are included. The measured HO2 can only be explained by the model, when NO concentrations at night of around 5 ppt are assumed to be present. The presence of HO2 radicals implies the presence of hydroxyl radicals at night in concentrations of up to 105 cm–3.  相似文献   

7.
A discharge-flow tube coupled with resonance fluorescence and chemiluminescence detection has been used to investigate the reactions IO + HO2 products (1) and IO + O(3P) I + O2(2), at T = 296 ± 1 K and P = 1.7 - 2 Torr. The rate constants k-1 and k2 have been found to be (7.1 ± 1.6) × 10-11 cm3 molecule-1 s-1 and (1.35 ± 0.15) × 10-10 cm3 molecule-1 s-1, respectively.  相似文献   

8.
Vertical profiles of stratospheric HO2 and NO2 concentrations were determined using matrix isolation and ESR. Up to 10 different samples per flight were collected in situ by a balloon borne cryosampler. Free radicals and trace constituents which are condensable at 68 K are trapped in a polycristalline H2O or D2O matrix. After collection, the samples are stored at a temperature below 83 K until they are analysed in the laboratory by X-band ESR spectroscopy at 4 K. The HO2 and NO2 were identified and calibrated by comparison with standard samples collected in the laboratory under typical stratospheric sampling conditions. From several flights over Southern France (44°N) we obtained two profiles of the stratospheric NO2 mixing ratio. One, from 21 October 1982, agrees well with previous measurements. The other, from 8 October 1981, is lower by one order of magnitude. The few HO2 data obtained around 35 km altitude agree with previous measurements. An isolated measurement at 17 km altitude is one order of magnitude higher than the model predicted HO2 concentration.  相似文献   

9.
The impact of natural and anthropogenicnon-methane hydrocarbons (NMHC) on troposphericchemistry is investigated with the global,three-dimensional chemistry-transport model MOGUNTIA.This meteorologically simplified model allows theinclusion of a rather detailed scheme to describeNMHC oxidation chemistry. Comparing model resultscalculated with and without NMHC oxidation chemistryindicates that NMHC oxidation adds 40–60% to surfacecarbon monoxide (CO) levels over the continents andslightly less over the oceans. Free tropospheric COlevels increase by 30–60%. The overall yield of COfrom the NMHC mixture considered is calculated to beabout 0.4 CO per C atom. Organic nitrate formationduring NMHC oxidation, and their transport anddecomposition affect the global distribution of NO x and thereby O3 production. The impact of theshort-lived NMHC extends over the entire tropospheredue to the formation of longer-lived intermediateslike CO, and various carbonyl and carboxyl compounds.NMHC oxidation almost doubles the net photochemicalproduction of O3 in the troposphere and leads to20–80% higher O3 concentration inNO x -rich boundarylayers, with highest increases over and downwind ofthe industrial and biomass burning regions. Anincrease by 20–30% is calculated for the remotemarine atmosphere. At higher altitudes, smaller, butstill significant increases, in O3 concentrationsbetween 10 and 60% are calculated, maximizing in thetropics. NO from lightning also enhances the netchemical production of O3 by about 30%, leading to asimilar increase in the global mean OH radicalconcentration. NMHC oxidation decreases the OH radicalconcentrations in the continental boundary layer withlarge NMHC emissions by up to 20–60%. In the marineboundary layer (MBL) OH levels can increase in someregions by 10–20% depending on season and NO x levels.However, in most of the MBL OH will decrease by10–20% due to the increase in CO levels by NMHCoxidation chemistry. The large decreases especiallyover the continents strongly reduce the markedcontrasts in OHconcentrations between land and oceanwhich are calculated when only the backgroundchemistry is considered. In the middle troposphere, OHconcentrations are reduced by about 15%, although dueto the growth in CO. The overall effect of thesechanges on the tropospheric lifetime of CH4 is a 15%increase from 6.5 to 7.4 years. Biogenic hydrocarbonsdominate the impact of NMHC on global troposphericchemistry. Convection of hydrocarbon oxidationproducts: hydrogen peroxides and carbonyl compounds,especially acetone, is the main source of HO x in theupper troposphere. Convective transport and additionof NO from lightning are important for the O3 budgetin the free troposphere.  相似文献   

10.
A new version of an atmospheric pressure chemical ionisation mass spectrometer has been developed for ground based in situ atmospheric measurements of OH and total peroxy (HO2 + organic peroxy) radicals. Based on the previously developed principle of chemical conversion of OH radicals to H2SO4 in reaction with SO2 and detection of H2SO4 using an ion molecule reaction with NO3─, the new instrument is equipped with a turbulent chemical conversion reactor allowing for measurements in moderately polluted atmosphere at NO concentrations up to several ppb. Unlike other similar devices, where the primary NO3─ ions are produced using radioactive ion sources, the new instrument is equipped with a specially developed corona discharge ion source. According to laboratory measurements, the overall accuracy and detection limits are estimated to be, respectively, 25% and 2 × 105 molecule cm-3 for OH and 30% and 1 × 105 molecule cm-3 for HO2 at 10 min integration times. The detection limit for measurements of OH radicals under polluted conditions is 5 × 105 molecules cm-3 at 10 min integration times. Examples of ambient air measurements during a field campaign near Paris in July 2007 are presented demonstrating the capability of the new instrument, although with reduced performance due to the employment of non isotopic SO2.  相似文献   

11.
Photochemical box modelling was undertaken to investigate OH and HO2 radical chemistry during summer and winter field campaigns in the urban city-centre of Birmingham in the UK. The model employed the most recent version of the Master Chemical Mechanism (v3.1) and was constrained to 15-minute average measurements of long-lived species determined in situ at the site. The model was used to predict OH and HO2 concentrations for comparison with measurements made by the fluorescence assay by gas expansion technique. Whilst there was generally good agreement between the modelled and measured OH concentrations, particularly during summer, there was sometimes a significant model under-prediction during daylight hours, which significantly skews the overall model: measured agreement. There were less measured data available for HO2, but the agreement between model and measurement for the days where measurements existed were less good than for OH, with one or two exceptions. The modelled:measured ratios between the hours of 11:00–15:00 h for OH were 0.58 and 0.50 for summer and winter respectively. For HO2, the same ratios were 0.56 in the summer and 0.49 in the winter. Sensitivity studies were conducted to attempt to understand the model-measurement discrepancy. The predicted radical concentrations were particularly sensitive to changes in NOX concentrations. Constraining the model to the observed HO2 concentrations made the OH predictions worse. These results highlight the fact that there are many complexities in urban areas and that more highly-instrumented campaigns are required in the future to further our understanding.  相似文献   

12.
We use a global atmospheric chemistry transport model to study the possible influence of aqueous phase reactions of peroxynitric acid (HNO4) on the concentrations and budgets of NOx, SOx, O3 and H2O2. Laboratory studies have shown that the aqueous reaction of HNO4aq withHSO– 3aq, and the uni-molecular decomposition of the NO4 – anion to form NO2 – (nitrite) occur on a time scale of about a second. Despite a substantial contribution of the reaction of HSO– 3aq with HNO4aq to the overall in-cloud conversion of SO2 to SO4 2–, a simultaneous decrease of other oxidants (most notably H2O2) more than compensated the increase in SO4 2– production. The strongest influence of heterogeneous HNO4 chemistry was found in the boundary layer, where calculated monthly average ozone concentrations were reduced between 2% to 10% andchanges of H2O2 between –20% to +10%compared to a simulation which ignores this reaction. Furthermore, SO2 was increased by 10% to 20% and SO4 2–depleted by up to 10%. Since the resolution of our global model does not enable a detailed comparison with measurements in polluted regions, it is not possible to verify whether considering heterogeneous HNO4 reactions results in a substantial improvement of atmospheric chemistry transport models. However, the conversion of HNO4 in the aqueous phase seems to be efficient enough to warrant further laboratory investigations and more detailed model studies on this topic.  相似文献   

13.
A bifurcation phenomenon with relevance to atmospheric chemistry is discussed. The gasphase reactions in the troposphere exhibit two types of temporal evolution which are controlled by the strength of the source,Q, of nitric oxide, NO, via the nonlinear chemical coupling between the hydrogen oxides and nitrogen oxides chemistry. IfQ remains below a threshold value, all short-lived species, including NO, approach steady-state concentrations, while above the threshold bifurcation to another state with increasing (nonstationary) NO concentrations accompanied by a depletion of the OH and HO2 abundances takes place.  相似文献   

14.
The Models-3 Community Multi-scale Air Quality modeling system (CMAQ) coupled with the Regional Atmospheric Modeling System (RAMS) is used to simulate three-dimensional concentration distributions of hydroxyl (OH) and hydroperoxyl (HO2) radicals over the western Pacific Ocean during the NASA Transport and Chemical Evolution over the Pacific (TRACE-P) field campaign. Modeled values of OH and HO2 and their closely related chemical species and photolysis rates are compared with observational data collected onboard the DC-8 aircraft. Comparison shows that the model reasonably reproduced these observed values over a broad range of conditions with an overall tendency to overestimate the measured OH and HO2 by a factor of 1.56 and 1.24, respectively. A case study of OH, HO2 and their closely related chemical species and photolysis rates along the DC-8 flights 11 and 12 conducted on 17–18 March 2001 shows that the model reproduces the temporal and spatial variations reasonable well, and produces more reliable OH and HO2 concentrations in the polluted environment than in the clean marine boundary layer.  相似文献   

15.
A cryogenic system for the airborne and ground based sampling of ambient radicals by matrix isolation is described. The trapped radicals, e.g., NO2 and RO2, are analyzed by ESR. The technique has been improved, mainly by addition of water vapor to the sampled air, to yield a collection efficiency of (90±10)% and a lower detection limit of about 20 ppt, but it still does not distinguish between the different RO2. Careful calibration reduced the measurement error (1 ) to ±10% for NO2 and ±15% for HO2. Two diurnal variations of RO2 and NO2 at ground level and vertical profiles in the lower troposphere are presented.  相似文献   

16.
As part of the Polar Sunrise Experiment (PSE) 1997, concentrations of halogen species thought to be involved in ground level Arctic ozone depletion were made at Alert, NWT, Canada (82.5°N, 62.3°W) during the months of March and April, 1997. Measurements were made of photolyzable chlorine (Cl2 and HOCl) and bromine (Br2 and HOBr) using the Photoactive Halogen Detector (PHD), and bromine radicals (BrOx) using a modified radical amplifier. During the sampling period between Julian Day 86 (March 27) and Day 102 (April 12), two ozone depletion episodes occurred, the most notable being on days 96-99, when ozone levels were below detectable limits (1 ppbv). Concentrations of BrOx above the 4 pptv detection limit were found for a significant part of the study, both during and outside of depletion events. The highest BrOx concentrations were observed at the end of the depletion event, when the concentration reached 15 pptv. We found substantial amounts of Br2 in the absence of O3, indicating that O3 is not a necessary requirement for production of Br2. There is also Br2 present when winds are from the south, implying local scale (e.g. from the snowpack) production. During the principal O3 depletion event, the HOBr concentration rose to 260 pptv, coincident with the BrOx maximum. This implies a steady state HO2 concentration of 6 pptv. During a partial O3 depletion event, we estimate that the flux of Br2 from the surface is about 10 times greater than that for Cl2.  相似文献   

17.
The HO x (OH and HO2) production rate in indoor air caused by radon decay was measured by the chemical amplification technique. The average HO x production rate was found to be (4.31±0.07)×105 HO x per Rn decay per second (Bq) within the range of relative humidity from 3.4 to 55.0 percent at 22 °C. This work providedG(HO x )-value, 7.86±0.13 #/100 eV in air by directly measuring [HO x ] from radiolysis of water vapor. It is also found that there is no obvious relationship between the HO x production rate and the relative humidity in this range. Therefore, this work provides both the basic data for the evaluation of radioactive pollution in indoor air as well as a potentially useful way to produce HO x concentrations in air.  相似文献   

18.
Reported are the results from a comparison of OH,H2O2CH3OOH, and O3 observationswithmodel predictions based on current HOx–CH4reaction mechanisms. The field observations are thoserecorded during the NASA GTE field program, PEM-Tropics A. The major focus ofthis paper is on thosedata generated on the NASA P-3B aircraft during a mission flown in the marineboundary layer (MBL) nearChristmas Island, a site located in the central equatorial Pacific (i.e.,2° N, 157° W). Taking advantage of thestability of the southeastern trade-winds, an air parcel was sampled in aLagrangian mode over a significantfraction of a solar day. Analyses of these data revealed excellent agreementbetween model simulated andobserved OH. In addition, the model simulations reproduced the major featuresin the observed diurnalprofiles of H2O2 and CH3OOH. In the case ofO3, the model captured the key observational feature whichinvolved an early morning maximum. An examination of the MBL HOxbudget indicated that the O(1D) + H2Oreaction is the major source of HOx while the major sinks involveboth physical and chemical processes involving the peroxide species,H2O2 and CH3OOH. Overall, the generally goodagreement between modeland observations suggests that our current understanding ofHOx–CH4 chemistry in the tropical MBL isquite good; however, there remains a need to critically examine this chemistrywhen both CH2O and HO2are added to the species measured.  相似文献   

19.
Generally, it is assumed that UV-light, high temperature or reactive molecules like O3 and OH are needed to activate gas reactions in air. In consequence, the catalytic activity on natural materials such as sand and soil on the earth's surface is assumed to be insignificant. We have measured O2-dissociation rates on natural quartz sand at 40˚C and compared these with O2-dissociation rates near 500˚C on materials with well-known catalytic activity. In terms of probabilities for dissociation of impinging O2-molecules the measured rates are in the 10−12–10−4 range. We have also measured dissociation rates of H2 and N2, water-formation from H2 and O2 mixtures, exchange of N between N2, NO x and a breakdown of HNO3, NO2 and CH4 on natural quartz sand at 40˚C. The measured rates together with an effective global land area have been used to estimate the impact of thermodynamically driven reactions on the earth's surface on the global atmospheric budgets of H2, NO2 and CH4. The experimental data on natural quartz sand together with data from equilibrium calculations of air suggest that an expected increase in anthropogenic supply of air pollutants, such as NO x or other “reactive” nitrogen compounds, hydrogen and methane, will be counter-acted by catalysis on the earth's surface. On the other hand, at Polar Regions and boreal forests where the “reactive” nitrogen concentration is below equilibrium, the same catalytic effect activates formation of bio-available nitrogen compounds from N2, O2 and H2O.  相似文献   

20.
Lightning is thought to represent an important source of tropospheric reactive nitrogen species NOx (NO + NO2),but estimates of global production of NOx by lightning varyconsiderably. We evaluate the production of NOx by lightning using a global chemical/transport model, satellite lightning observations, and airborne NOx measurements. Various model calculations are conducted toassess the global NOx production rate of lightning by comparing the model calculations with airborne measurements. The results show that the simulated NOx in the tropical middle and upper troposphere are very sensitiveto the amount and altitude of the lightning NOx used in the model. A global lightning NOx production of 7 Tg N yr–1uniformly distributed in convective clouds or 3.5 Tg N yr–1 distributedin the upper cloud regions produces good agreement between calculated and measured NOx concentrations in the tropics.  相似文献   

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