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1.
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   

2.
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3.
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   

4.
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   

5.
There are large uncertainties in identifying and quantifying the natural and anthropogenic sources of chloromethanes – methyl chloride (CH3Cl), chloroform (CHCl3) and dichloromethane (CH2Cl2), which are responsible for about 15% of the total chlorine in the stratosphere. We report two years of in situ observations of these species from the AGAGE (Advanced Global Atmospheric Gas Experiment) program at Cape Grim, Tasmania (41° S, 145° E). The average background levels of CH3Cl, CHCl3 and CH2Cl2 during 1998–2000 were 551± 8, 6.3± 0.2 and 8.9± 0.2 ppt (dry air mole fractions expressed in parts per 1012) respectively, with a two-year average amplitude of the seasonal cycles in background air of 25, 1.1 and 1.5 ppt respectively. The CH3Cl and CHCl3 records at Cape Grim show clear episodes of elevated mixing ratios up to 1300 ppt and 55 ppt respectively, which are highly correlated, suggesting common source(s). Trajectory analyses show that the sources of CH3Cl and CHCl3 that are responsible for these elevated observations are located in coastal-terrestrial and/or coastal-seawater regions in Tasmania and the south-eastern Australian mainland. Elevated levels of CH2Cl2 (up to 70 ppt above background) are associated mainly with emissions from the Melbourne/Port Phillip region, a large urban/industrial complex (population 3.5 million) 300 km north of Cape Grim.Now at the Centre for Atmospheric ChemistryNow at School of Environmental Sciences  相似文献   

6.
Measurements of the sum of peroxy radicals [HO2 + RO2],NOx (NO + NO2) and NOy (the sum of oxidisednitrogen species) made at Mace Head, on the Atlantic coast of Ireland in summer 1996 and spring 1997 are presented. Together with a suite of ancillary measurements, including the photolysis frequencies of O3 O(1D)(j(O1D)) and NO2 (j(NO2)), the measured peroxy radicals are used to calculate meandailyozone tendency (defined as the difference of the in-situphotochemical ozone production and loss rates); these values are compared with values derived from the photochemical stationary state (PSS) expression. Although the correlation between the two sets of values is good, the PSS values are found to be significantly larger than those derived from the peroxy radical measurements, on average, in line with previous published work. Possible sources of error in these calculations are discussed in detail. The data are further divided up into five wind sectors, according to the instantaneous wind direction measured at the research station. Calculation of mean ozone tendencies by wind sector shows that ozone productivity was higher during spring (April–May) 1997 than during summer (July–August) 1996across all airmasses, suggesting that tropospheric photochemistry plays an important role in the widely-reported spring ozone maximum in the Northern Hemisphere. Ozone tendencies were close to zero for the relatively unpolluted south-west, west and north-west wind sectors in the summer campaign, whereas ozone productivity was greatest in the polluted south-east sector for both campaigns. Daytime weighted average ozone tendencies were +(0.3± 0.1) ppbv h–1 for summer 1996 and +(1.0± 0.5) ppbvh–1 for spring 1997. These figures reflect the higher mixing ratios of ozone precursors in spring overall, as well as the higher proportion of polluted air masses from the south-east arriving at the site during the spring campaign. The ozone compensation point, where photochemical ozone destruction and production processes are in balance, is calculated to be ca. 14 pptv NO for both campaigns.  相似文献   

7.
A novel method has been examined for monitoring tropospheric hydroxyl radicals (OH), the most important oxidant in tropospheric chemistry. Aqueous phase salicylic acid reacts with atmospheric OH to produce 2,5-dihydroxy benzoic acid (2,5-DHBA) and other products. High Performance Liquid Chromatography (HPLC) is used to separate the post-reaction solution and the products are quantified using fluorescence detection. Unlike other methods, it has been reported to be inexpensive, portable and relatively simple. Although the sensitivity was sufficient to measure typical daytime OH concentrations of 0.04–0.4 ppt., the method was hindered by numerous interferences. Successive identification and elimination of these still resulted in a signal that was much larger than expected. Tests showed that this was not likely to be due to ozone, HO2, NOx, H2O2, aerosols, light or bacteria. Experimental and numerical studies suggest that the interference could be due to methyl peroxy radicals. The effect of many other components in the atmosphere, both individual and combined, must also be tested before the method can be used reliably in the field. The validity of previous reports of ambient hydroxyl measurements using this technique is therefore brought into question.  相似文献   

8.
Free Radicals and Fast Photochemistry during BERLIOZ   总被引：4，自引：0，他引：4  
The free radicals OH, HO2, RO2, and NO3 are known to be the driving force for most chemical processes in the atmosphere. Since the low concentration of the above radicals makes measurements particularly difficult, only relatively few direct measurements of free radical concentrations have been reported to date.We present a comprehensive set of simultaneous radical measurements performed by Laser Induced Fluorescence (LIF), Matrix Isolation –Electron spin Resonance (MI-ESR), Peroxy Radical Chemical Amplification (PERCA), and Differential Optical Absorption Spectroscopy (DOAS) during the BERLIner OZonexperiment (BERLIOZ) during July and August of 1998 near Berlin, Germany. Most of the above radical species were measured by more than one technique and an intercomparison gave good agreement. This data set offered the possibility to study and quantify the role of each radical at a rural, semi-polluted site in the continental boundary layer and to investigate interconnections and dependencies among these free radicals.In general (box) modelled diurnal profiles of the different radicals reproduced the measurements quite well, however measured absolute levels are frequently lower than model predictions. These discrepancies point to disturbing deficiencies in our understanding of the chemical system in urban air masses.In addition considerable night-time peroxy radical production related to VOC reactions with NO3 and O3 could be quantified.  相似文献   

9.
An instrument is developed for the measurement of peroxy radical using chemical amplification coupled with NO2-luminol chemiluminescence detection. The chain length of 147 ± 10 (1σ) is determined by an HO2 source that uses the photolysis of water vapor under 184.9 nm in air. A Nafion system equipped with a Nafion tube of ~2.2 mm external diameter and 350 mm length is employed in the PERCA instrument (Nafion-PERCA system). When flowing an air sample containing HO2 through the Nafion system, it is found that - 94.6 % of HO2 is removed. In contrast, only 17.8 % of RO2 radicals (a mixtures of CH3O2 and CH3C(O)O2 with a ratio of 1.1:0.9) are removed. The results indicate the Nafion system has a good selective removing performance of HO2 radical during the PERCA measurement. Therefore, the method could be applied to ambient and laboratory measurements of absolute concentrations of RO2 as well as the sum of HO2 and RO2.  相似文献   

10.
Barnes  I.  Bastian  V.  Becker  K. H.  Fink  E. H.  Nelsen  W. 《Journal of Atmospheric Chemistry》1986,4(4):445-466
The reactions of OH radicals with SO2, H2S, thiophenol, and a series of aliphatic thiols (1–5 C-atoms) have been investigated in 201 and 381 reaction chambers at 1 atm total pressure and 300 K using a competitive kinetic technique. Initially, OH radicals were produced by photolysis of CH3ONO/NO mixtures in air. Applying this OH source rate constants for OH with SO2, H2S, and thiophenol in synthetic air were determined to be (1.1±0.2)×10-12, (5.5±0.8)×10-12 and (1.1±0.2)×10-11 cm3 s-1, respectively. However, when this method was applied to the aliphatic thiols the rate constants obtained were found to be dependent on the partial pressures of O2 and NO. These effects have been attributed to the built-up of a radical species, not yet identified, which leads to uncontrolled chain reactions in the system. Using the photolysis of H2O2 at wavelengths greater than 260 nm as the OH source in 1 atm N2, rate constants for the 1–5 aliphatic thiols in the range 2.9 to 5.6×10-11 cm3 s-1 were obtained. The rate constants obtained in the present study are compared with recent literature values.  相似文献   

11.
Measurements of total peroxy radicals (HO2?+?RO2) and nitrate radical (NO3) were made on the NOAA research vessel R/V?Brown along the U.S. Gulf Coast during the TexAQS 2006 field campaign. The measurements were modelled using a constrained box-model based upon the Master Chemical Mechanism (MCM). The agreement between modelled and measured HO2?+?RO2 was typically within ??40% and, in the unpolluted regions, within 30%. The analysis of the model results suggests that the MCM might underestimate the concentrations of some acyl peroxy radicals and other small peroxy radicals. The model underestimated the measurements of NO3 by 60?C70%, possibly because of rapid heterogeneous uptake of N2O5. The MCM model results were used to estimate the composition of the peroxy radical pool and to quantify the role of DMS, isoprene and alkenes in the formation of RO2 in the different regions. The measurements of HO2?+?RO2 and NO3 were also used to calculate the gas-phase budget of NO3 and quantify the importance of organic peroxy radicals as NO3 sinks. RO2 accounted, on average, for 12?C28% of the total gas-phase NO3 losses in the unpolluted regions and for 1?C2% of the total gas-phase NO3 losses in the polluted regions.  相似文献   

12.
The reactions of the alkanes under atmospheric conditions and in the presence of oxides of nitrogen are reviewed and evaluated. Particular emphasis is placed upon their subsequent reactions after the initial OH radical reaction under conditions where the alkyl peroxy radicals produced react predominantly with NO, rather than with HO2 and/or RO2 radicals. Methods are discussed for estimating the overall OH radical rate constants, the number of molecules of NO consumed per alkane molecule reacted, and the products formed and their yields.  相似文献   

13.
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   

14.
Concentrations of peroxy radicals were measured by a chemical amplification technique at a remote forested site as part of the Program for Research on Oxidants in a Forested Region in Nikko (PROFRN). During the measurement period of 22–27 July 2002, the mixing ratios of peroxy radicals averaged for 3 min at midday ranged from 109 to 134 pptv at a height approximately 5 m above the forest canopy. Significant diurnal variation in concentrations of peroxy radicals was observed, with the maximum usually occurring around noon. Most of the variation was driven by changes in the intensity of solar radiation. However, it was found that the peroxy radical concentration reached its peak about 3-h later than that of solar radiation on 24 and 26 July. The origins of this delay are discussed based on an analysis of the total radical budget in that period. A transport of polluted air masses to the site was one of possible causes for the inconsistency. In addition, the measured peroxy radical concentrations were compared with those derived from the deviations of NO-NO2-O3 photo-stationary state (PSSD) for clear days. The estimated half-hour-average concentrations of peroxy radical were in agreement with the PERCA measured in the morning and late afternoon. However the two techniques differed by as much as a factor of two during the time of near midday.  相似文献   

15.
Improvements of the matrix isolation/electron spin resonance technique for the measurement of NO2, NO3, and RO2 radicals in the atmosphere are described. The use of D2O instead of H2O as the matrix yields a better spectral resolution and, as a consequence, larger a signal-to-noise ratio as well as better identification of the different species. Reference spectra of the different radicals in H2O and D2O matrices are compared. While a large degree of correlation exists amongst the spectra of the different (unsubstituted and substituted) alkylperoxy radicals, the spectra of HO2, CH3C(O)O2, and NO3 show significant differences that allow their distinction in atmospheric samples.A numerical procedure for the analysis of the composite ESR spectra obtained from atmospheric samples was developed. Subtraction of the dominant NO2 signal is performed by matching a reference NO2 spectrum with respect to amplitude, spectral position, and line width to the sample spectrum. The manipulations are performed with the virtually noise-free reference spectrum and are based on physical information. The residual spectrum is then analyzed for RO2 (and/or NO3) by simultaneously fitting up to six different reference spectra.The method was applied to laboratory samples as well as to atmospheric samples in order to demonstrate the ability of retrieving small amounts of HO2 in the presence of large amounts of NO2 and other peroxy radicals. The new algorithm allowed, for the first time, the identification of the HO2 and CH3C(O)O2 radical in tropospheric air at concentrations ranging up to 40 ppt.  相似文献   

16.
Reactive halogen species (RHS = X, XO, HOX, OXO; X = Cl, Br, I) are known to have an important influence on the chemistry in the polar boundary layer (BL), where they are responsible for ozone depletion events in spring. Recent field campaigns at Mace Head, Ireland, and the Dead Sea, Israel, identified for the first time iodine oxide (IO) at mixing ratios of up to 6.6 ppt and 90 ppt bromine oxide (BrO), respectively, by DOAS also at lower latitudes. These results intensified the discussion about the role of the RHS in the mid-latitude BL.Photochemical box model calculations show that the observed IO mixing ratios can destroy ~0.45 ppb ozone per hour. This is comparable to the rates of the known O3-loss processes in the boundary layer. The model studies also reveal that IO, at these levels, has a strong influence on the BL photochemistry, increasing the OH/HO2- and the NO2/NO - ratios. In combination these changes lead to a reduction of the photochemical ozone formation, which - in addition - reduces ozone mixing ratios by up to 0.15 ppb/h.The studies for the Dead Sea case give no information on the heterogeneous process responsible for the bromine release, but they show that a total of 2 – 4 ppb of total bromine have to be released to explain the observed complete depletion of 60 ppb ozone in 2 – 3 hours.  相似文献   

17.
Alkyl nitrate yields from the NO x photooxidations of neopentane, 2-methylbutane and 3-methylpentane have been determined over the temperature and pressure ranges 281–323 K and 54–740 torr, respectively. The formation of the alkyl nitrates is attributed to the reaction pathway (1b) $${\text{RO}}_{\text{2}} + {\text{NO}}^{{\text{ }}\underrightarrow {\text{M}}} {\text{ RONO}}_{\text{2}}$$ and rate constant ratios k 1b/(k 1a+k 1b) are estimated, where (1a) is the reaction pathway (1a) $${\text{RO}}_{\text{2}} + {\text{NO}} \to {\text{RONO}}_{\text{2}} .$$ A method for estimating this rate constant ratio for primary, secondary and tertiary alkyl peroxy radicals is presented.  相似文献   

18.
Kinetics and products of the gas-phase reactions of dimethylsulphide (DMS), dimethylsulphoxide (DMSO) and dimethylsulphone (DMSO2) with Br atoms and BrO radicals in air have beeninvestigated using on-line Fourier Transform Infrared Spectroscopy (FT-IR) as analytical technique at 740 ± 5 Torr total pressure and at 296 ± 3 K in a480 L reaction chamber. Using a relative rate method for determining the rate constants; the following values (expressed in cm3molecule–1 s–1) were found: kDMS+Br = (4.9 ±1.0) ×10–14, kDMSO + Br < 6 × 10–14,kDMSO 2 + Br 1 × 10–15,kDMSO + BrO = (1.0 ± 0.3) × 10–14 andkDMSO 2 + BrO 3 × 10–15 (allvalues are given with one on the experimental data). DMSO, SO2, COS, CH3SBr andCH3SO2Br were identified as the main sulphur containing products of the oxidation of DMS by Br atoms. From the reaction between DMSO and Br atoms, DMSO2and CH3SO2Br were the only sulphur containing products thatwere identified. DMSO, DMSO2 and SO2 were identified as themain sulphur containing products of the reaction between DMS and BrO.DMSO2 was found to be the only product of the reaction between DMSO and BrO. For the reactions of DMSO2 with Br and BrO no products were identified because the reactions were too slow.The implications of these results for atmospheric chemistry are discussed.  相似文献   

19.
As part of the LBA-CLAIRE-98 experiment, ground level atmosphericconcentrations of O3, CO, hydroperoxides and organic acids weremeasured in the rainforest region in Surinam. Measurements of CO andO3 were also made at a coastal site.The results suggest that a significant consumption of `boundary layer' ozoneoccurs over the forested region of Surinam, with an estimated net ozoneconsumption of about 5% hr–1 during daytime. Thiswould be mainly explained by a low photochemical production and high drydeposition to the forest vegetation. Compared to other tropical sites, lowerlevels of H2O2 were observed at the rainforest site,with an average boundary layer concentration of 0.55± 0.2 nmolmol–1. Also acetic and formic acids showed relatively lowaverage boundary layer mixing ratios; 1.1± 0.4 nmolmol–1 and 1.4± 0.5 nmol mol–1,respectively. Significant correlations were found between both acids andbetween the acids and hydrogen peroxide, suggesting an atmospheric source forthe acids.From the available observations we discuss possible implications of ourmeasurements for the O3, HO2, and NOx budgetsand concentrations in the boundary layer. We conclude that, despite the highsolar irradiation, relatively low levels of O3,H2O2, HCOOH and CH3COOH are observed in theboundary layer of the rainforest of Surinam, probably due to low levels ofNOx and high levels of VOCs, which leads to loss of OH andHO2 radicals. Additionally, high deposition rates of these gasesoccur to the forest vegetation.  相似文献   

20.
The 1,4-hydroxycarbonyl 5-hydroxy-2-pentanone is an important product of the gas-phase reaction of OH radicals with n-pentane in the presence of NO. We have used a relative rate method with 4-methyl-2-pentanone as the reference compound to measure the rate constant for the reaction of OH radicals with 5-hydroxy-2-pentanone at 296 ± 2 K. The carbonyls were sampled by on-fiber derivatization using a Solid Phase Micro Extraction (SPME) fiber coated with O> -(2,3,4,5,6-pentafluorobenzyl)hydroxylamine hydrochloride with subsequent thermal desorption of the oxime derivatives and quantification by gas chromatography with flame ionization detection. For comparison, the reference compound was also analyzed following sample collection onto a Tenax adsorbent cartridge. Products of the reaction were investigated using coated-fiber SPME sampling with gas chromatography-mass spectrometry analysis as well as by using in situ atmospheric pressure ionization mass spectrometry. A rate constant for the reaction of OH radicals with 5-hydroxy-2-pentanone of (1.6 ± 0.4) × 10–11 cm3 molecule–1 s–1 was obtained at 296 ± 2 K. Two dicarbonyl products, of molecular weight 86 and 100, were observed and are attributed to CH3C(O)CH2CHO and CH3C(O)CH2CH2CHO, respectively. Reaction schemes leading to these products are presented.  相似文献   

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