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1.
Local ozone production and loss rates for the arctic free troposphere (58–85° N, 1–6 km, February–May) during the TroposphericOzone Production about the Spring Equinox (TOPSE) campaign were calculated using a constrained photochemical box model. Estimates were made to assess the importance of local photochemical ozone production relative to transport in accounting for the springtime maximum in arctic free tropospheric ozone. Ozone production and loss rates from our diel steady-state box model constrained by median observations were first compared to two point box models, one run to instantaneous steady-state and the other run to diel steady-state. A consistent picture of local ozone photochemistry was derived by all three box models suggesting that differences between the approaches were not critical. Our model-derived ozone production rates increased by a factor of 28 in the 1–3 km layer and a factor of 7 in the 3–6 kmlayer between February and May. The arctic ozone budget required net import of ozone into the arctic free troposphere throughout the campaign; however, the transport term exceeded the photochemical production only in the lower free troposphere (1–3 km) between February and March. Gross ozone production rates were calculated to increase linearly with NOx mixing ratiosup to 300 pptv in February and for NOx mixing ratios up to 500 pptv in May. These NOx limits are an order of magnitude higher thanmedian NOx levels observed, illustrating the strong dependence ofgross ozone production rates on NOx mixing ratios for the majority of theobservations. The threshold NOx mixing ratio needed for netpositive ozone production was also calculated to increase from NOx 10pptv in February to 25 pptv in May, suggesting that the NOx levels needed to sustain net ozone production are lower in winter than spring. This lower NOx threshold explains how wintertime photochemical ozone production can impact the build-up of ozone over winter and early spring. There is also an altitude dependence as the threshold NOx neededto produce net ozone shifts to higher values at lower altitudes. This partly explains the calculation of net ozone destruction for the 1–3 km layerand net ozone production for the 3–6 km layer throughout the campaign.  相似文献   

2.
Simultaneousindependent measurements of NOy and NOx(NOx= NO + NO2) by high-sensitivitychemiluminescence systems and of PAN (peroxyacetylnitrate) and PPN (peroxypropionyl nitrate) by GC-ECDwere made at Spitsbergen in the Norwegian Arcticduring the first half year of 1994. The average mixingratio of the sum of PAN and PPN (denoted PANs)increased from around 150 pptv in early winter to amaximum of around 500 pptv in late March, whereasepisodic peak values reached 800 pptv. This occurredsimultaneously with a maximum in ozone which increasedto 45–50 ppbv in March–April. The average NOxmixing ratio was 27 pptv and did not show any cyclethrough the period. The NOy mixing ratio showeda maximum in late March, while the difference betweenNOy and PAN decreased during spring. This is anindication of the dominance of PAN in the NOybudget in the Arctic, but possible changes in theefficiency of the NOy converter could alsocontribute to this. Although most PAN in theArctic is believed to be due to long range transport,the observations indicate local loss and formationrates of up to 1–2 pptv h-1 in April–May.Measurements of carbonyl compounds suggest thatacetaldehyde was the dominant, local precursor ofPAN.Now at 1.  相似文献   

3.
Recent observations suggest that the abundance of ozone between 2 and 8 km in the Northern Hemisphere mid-latitudes has increased by about 12% during the period from 1970 to 1981. Earlier estimates were somewhat more conservative suggesting increases at the rate of 7% per decade since the start of regular observations in 1967. Previous photochemical model studies have indicated that tropospheric ozone concentrations would increase with increases in emissions of CO, CH4 and NO x . This paper presents an analysis of tropospheric ozone which suggests that a significant portion of its increase may be attributed to the increase in global anthropogenic NO x emissions during this period while the contribution of CH4 to the increase is quite small. Two statistical models are presented for estimating annual global anthropogenic emissions of NO x and are used to derive the trend in the emissions for the years 1966–1980. These show steady increase in the emissions during this interval except for brief periods of leveling off after 1973 and 1978. The impact of this increase in emissions on ozone is estimated by calculations with a onedimensional (latitudinal) model which includes coupled tropospheric photochemistry and diffusive meridional transport. Steady-state photochemical calculations with prescribed NO x emissions appropriate for 1966 and 1980 indicate an ozone increase of 8–11% in the Northern Hemisphere, a result which is compatible with the rise in ozone suggested by the observations.  相似文献   

4.
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   

5.
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   

6.
A series of ozone transects measured each year from 1987 to 1990 over thewestern Pacific and eastern Indian oceans between mid-November andmid-Decembershows a prominent ozone maximum reaching 50–80 ppbv between 5 and 10 kmin the 20° S–40° S latitude band. This maximum contrasts with ozonemixing ratios lower than20 ppbv measured at the same altitudes in equatorial regions. Analyses witha globalchemical transport model suggest that these elevated ozone values are part ofa large-scale tropospheric ozone plume extending from Africa to the western Pacific acrosstheIndian ocean. These plumes occur several months after the peak in biomassburninginfluence and during a period of high lightning activity in the SouthernHemispheretropical belt. The composition and geographical extent of these plumes aresimilar to theozone layers previously encountered during the biomass burning season in thisregion.Our model results suggest that production of nitrogen oxides from lightningstrokes sustains the NOx (= NO+NO2) levels and the ozonephotochemical productionrequired in the upper troposphere to form these persistent elevated ozonelayers emanating from biomass burning regions.  相似文献   

7.
The response of tropospheric ozone to a change in solar UV penetration due to perturbation on column ozone depends critically on the tropospheric NO x (NO+NO2) concentration. At high NO x or a polluted area where there is net ozone production, a decrease in column ozone will increase the solar UV penetration to the troposphere and thus increase the tropospheric ozone concentration. However, the opposite will occur, for example, at a remote oceanic area where NO x is so low that there is net ozone destruction. This finding may have important implication on the interpretation of the long term trend of tropospheric ozone. A change in column ozone will also induce change in tropospheric OH, HO2, and H2O2 concentrations which are major oxidants in the troposphere. Thus, the oxidation capacity and, in turn, the abundances of many reduced gases will be perturbed. Our model calculations show that the change in OH, HO2, and H2O2 concentrations are essentially independent of the NO x concentration.  相似文献   

8.
Surface ozone data from 25 Europeanlow-altitude sites and mountain sites located between79°N and 28°N were studied. The analysiscovered the time period March 1989–February 1993.Average summer and winter O3 concentrations inthe boundary layer over the continent gave rise togradients that were strongest in the north-west tosouth-east direction and west-east direction, respectively. WintertimeO3 ranged from 19 to 27 ppbover the continent, compared to about 32 ppb at thewestern border, while for summer the continentalO3 values ranged between 39 and 56 ppb and theoceanic mixing ratios were around 37 ppb. In the lowerfree troposphere average wintertime O3 mixingratios were around 38 ppb, with only an 8 ppbdifference between 28°N and 79°N. For summerthe average O3 levels decreased from about 55 ppbover Central Europe to 32 ppb at 79°N. Inaddition, O3 and Ox(= O3 + NO2)in polluted and clean air were compared. Theamplitudes of the seasonal ozone variations increasedin the north-west to south-east direction, while thetime of the annual maximum was shifted from spring (atthe northerly sites) to late summer (at sites inAustria and Hungary), which reflected the contributionof photochemical ozone production in the lower partsof the troposphere.  相似文献   

9.
Growth in subsonic air traffic over the past 20 years has been dramatic, with an annual increase of }6.1% over the decade between 1978 and 1988. Furthermore, aircraft activities in the year 2000 are predicted to be double those of 1990, with a shift towards more high-flying, longhaul subsonics. Aircraft exhaust gases increase the amount of nitrogen oxides (NO x ) in the upper troposphere/lower stratosphere through injection at cruise altitudes. Given that NO x is instrumental in tropospheric ozone production and stratospheric ozone destruction, it is important to determine the influence of subsonic aircraft NO x emissions on levels of atmospheric ozone. This paper describes calculations designed to investigate the impact that subsonic aircraft may already have had on the atmosphere during the 1980s, run in a 2-D chemical-radiative-transport model. The results indicate a significant increase in upper tropospheric ozone over the decade arising from aircraft emissions. However, when comparing model results with observational data, certain discrepancies appear. Lower stratospheric ozone loss over the 1980s does not appear to be greatly altered by the inclusion of aircraft emissions in the model. However, given the trend in greater numbers of long-haul subsonic aircraft, this factor must be considered in any further calculations.  相似文献   

10.
The global three-dimensional Lagrangian chemistry-transport model STOCHEM has been used to follow the changes in the tropospheric distributions of the two major radiatively-active trace gases, methane and tropospheric ozone, following the emission of pulses of the short-lived tropospheric ozone precursor species, methane, carbon monoxide, NOx and hydrogen. The radiative impacts of NOx emissionswere dependent on the location chosen for the emission pulse, whether at the surface or in the upper troposphere or whether in the northern or southern hemispheres. Global warming potentials were derived for each of the short-lived tropospheric ozone precursor species by integrating the methane and tropospheric ozone responses over a 100 year time horizon. Indirect radiative forcing due to methane and tropospheric ozone changes appear to be significant for all of the tropospheric ozone precursor species studied. Whereas the radiative forcing from methane changes is likely to be dominated by methane emissions, that from tropospheric ozone changes is controlled by all the tropospheric ozone precursor gases, particularly NOxemissions. The indirect radiative forcing impacts of tropospheric ozone changes may be large enough such that ozone precursors should be considered in the basket of trace gases through which policy-makers aim to combat global climate change.  相似文献   

11.
Results from two air quality models (LOTOS, EURAD) have been used toanalyse the contribution of the different terms in the continuity equationto the budget of ozone, NOx and PAN. Both models cover largeparts of Europe and describe the processes relevant for troposphericchemistry and dynamics. One of the models is designed to simulate episodesin the order of 1–2 weeks (EURAD), the other is focussing on theseasonal scale (LOTOS). Based on EURAD simulations it is found that theatmospheric boundary layer (ABL) in Central Europe during a summer-smogepisode in 1990 acts as a source of ozone, which is partly exported from theproduction region in Central Europe. About 40% of the ozone producedchemically in the ABL is lost from Central Europe due to net transport(large-scale and turbulent), 40% are deposited within the domain. Vertical mass exchange of ozone is dominated by the prevailing subsidenceand averaged vertical mass fluxes are directed downward. Averaged massfluxes of PAN, which has no stratospheric source, are upward in the upperpart of the ABL. The results from LOTOS are discussed for the same episodeand for a two month period (July/August 1990). The budget calculation showlarger chemical production for the LOTOS model compared to EURAD. Therelative importance of deposition and net transport, however, is in the sameorder. Differences between the two-month calculation and the one weekepisode are only important for Western Europe where the chemical production is enhanced by 30% during the summer-smog episode. The dependence ofthe results on initial and boundary values is discussed for ozone on thebasis of a simple sensitivity study with EURAD where ozone in the FT is setto 10 ppb initially. This leads to a reversal in the direction of averagedozone mass fluxes in the upper part of the ABL.  相似文献   

12.
Measurements of NOx,y were made at Alert, Nunavut, Canada (82.5° N, 62.3° W) during surface layer ozone depletion events. In spring 1998, depletion events were rare and occurred under variable actinic flux, ice fog, and snowfall conditions. NOy changed by less than 10% between normal, partially depleted, and nearly completely depleted ozone air masses. The observation of a diurnal variation in NOx under continuous sunlight supports a source from the snowpack but with rapid conversion to nitrogen reservoirs that are primarily deposited to the surface or airborne ice crystals. It was unclear whether NOx was reduced or enhanced in different stages of the ozone depletion chemistry because of variations in solar and ambient conditions. Because ozone was depleted from 15–20 ppbv to less than 1 ppbv in just over a day in one event it is apparent that the surface source of NOx did not grossly inhibit the removal of ozone. In another case ozone was shown to be destroyed to less than the 0.5 ppbv detection limit of the instrument. However, simple model calculations show that the rate of depletion of ozone and its final steady-state abundance depend sensitively on the strength of the surface source of NOx due to competition from ozone production involving NOx and peroxy radicals. The behavior of the NO/NO2 ratio was qualitatively consistent with enhanced BrO during the period of active ozone destruction. The model is also used to emphasize that the diurnal partitioning of BrOx during ozone depletion events is sensitive to even sub ppbv variations in O3.  相似文献   

13.
The relationship between the emission of ozone precursors and the chemical production of tropospheric ozone(O3) in the Pearl River Delta Region(PRD) was studied using numerical simulation.The aim of this study was to examine the volatile organic compound(VOC)-or nitrogen oxide(NOx =NO+NO2)limited conditions at present and when surface temperature is increasing due to global warming,thus to make recommendations for future ozone abatement policies for the PRD region.The model used for this application is the U.S.Environmental Protection Agency’s(EPA’s) third-generation air-quality modeling system;it consists of the mesoscale meteorological model MM5 and the chemical transport model named Community Multi-scale Air Quality(CMAQ).A series of sensitivity tests were conducted to assess the influence of VOC and NOx variations on ozone production.Tropical cyclone was shown to be one of the important synoptic weather patterns leading to ozone pollution.The simulations were based on a tropicalcyclone-related episode that occurred during 14-16 September 2004.The results show that,in the future,the control strategy for emissions should be tightened.To reduce the current level of ozone to meet the Hong Kong Environmental Protection Department(EPD) air-quality objective(hourly average of 120 ppb),emphasis should be put on restricting the increase of NOx emissions.Furthermore,for a wide range of possible changes in precursor emissions,temperature increase will increase the ozone peak in the PRD region;the areas affected by photochemical smog are growing wider,but the locations of the ozone plume are rather invariant.  相似文献   

14.
The effects of deep convection on the potential for forming ozone (ozone production potential) in the free troposphere have been simulated for regions where the trace gas composition is influenced by biomass burning. Cloud dynamical and photochemical simulations based on observations in 1980 and 1985 Brazilian campaigns form the basis of a sensitivity study of the ozone production potential under differing conditions. The photochemical fate of pollutants actually entrained in a cumulus event of August 1985 during NASA/GTE/ABLE 2A (Case 1) is compared to photochemical ozone production that could have occurred if the same storm had been located closer to regions of savanna burning (Case 2) and forest burning (Case 3). In each case studied, the ozone production potential is calculated for a 24-hour period following convective redistribution of ozone precursors and compared to ozone production in the absence of convection. In all cases there is considerably more ozone formed in the middle and upper troposphere when convection has redistributed NOx, hydrocarbons and CO compared to the case of no convection.In the August 1985 ABLE 2A event, entrainment of a layer polluted with biomass burning into a convective squall line changes the free tropospheric cloud outflow column (5–13 km) ozone production potential from net destruction to net production. If it is assumed that the same cloud dynamics occur directly over regions of savanna burning, ozone production rates in the middle and upper troposphere are much greater. Diurnally averaged ozone production following convection may reach 7 ppbv/day averaged over the layer from 5–13 km-compared to typical free tropospheric concentrations of 25–30 ppbv O3 during nonpolluted conditions in ABLE 2A. Convection over a forested region where isoprene as well as hydrocarbons from combustion can be transported into the free troposphere leads to yet higher amounts of ozone production.  相似文献   

15.
The global three-dimensional Lagrangian chemistry-transport model STOCHEM has been used to follow changes in the tropospheric distributions of methane CH4 and ozone O3 following the emission of pulses of the oxides of nitrogen NO x . Month-long emission pulses of NO x produce deficits in CH4 mixing ratios that bring about negative radiative forcing (climate cooling) and decay away with e-folding times of 10–15 years. They also produce short-term excesses in O3 mixing ratios that bring about positive radiative forcing (climate warming) that decay over several months to produce deficits, with their attendant negative radiative forcing (climate cooling) that decays away in step with the CH4 deficits. Total time-integrated net radiative forcing is markedly influenced by cancellation between the negative CH4 and long-term O3 contributions and the positive short-term O3 contribution to leave a small negative residual. Consequently, total net radiative forcing from NO x emission pulses and the global warming potentials derived from them, show a strong dependence on the magnitudes, locations and seasons of the emissions. These dependences are illustrated using the Asian continent as an example and demonstrate that there is no simple robust relationship between continental-scale NO x emissions and globally-integrated radiative forcing. We find that the magnitude of the time-integrated radiative forcing from NO x -driven CH4 depletion tends to approach and outweigh that from ozone enhancement, leaving net time-integrated radiative forcings and global warming potentials negative (climate cooling) in contrast to the situation for aircraft NO x (climate warming). Control of man-made surface NO x emissions alone may lead to positive radiative forcing (climate warming).  相似文献   

16.
Several years of continuous measurements of surfaceozone at Norwegian monitoring sites are studied in aclimatological way. The monitoring sites are at rurallocations extending from 58°N, a few hundredkilometers from the European continent and into theArctic at 79°N. The ozone observations are sorted intoclasses of integrated NOx emissions along 96 h backtrajectories. The average seasonal cycles of ozone areestimated for each class separately. The differencesindicate the change from the background air due toanthropogenic emissions. The average seasonal cycle ofozone in the cleanest air masses showed a maximum inspring and a minimum during summer and autumn at allsites, but the spring maximum was more pronounced atthe southernmost locations. Polluted air masses showedan ozone deficit during winter and a surplus duringsummer. The deviation from the background was clearlylinked to the integrated NOx emission along thetrajectories. In summer the calculations indicate thatthe number of ozone molecules formed per NOx moleculedrops with increasing emissions. The average seasonalcycle of ozone at Birkenes for different transportsectors indicate that the most pronounced ozoneformation takes place in air masses from E-Europe/Russia.  相似文献   

17.
Measurements of NOx (NO +NO2) and the sum of reactive nitrogenconstituents, NOy, were made near the surface atAlert (82.5°N), Canada during March and April1998. In early March when solar insolation was absentor very low, NOx mixing ratios were frequentlynear zero. After polar sunrise when the sun was abovethe horizon for much or all of the day a diurnalvariation in NOx and NOy was observed withamplitudes as large as 30–40 pptv. The source ofactive nitrogen is attributed to release from the snowsurface by a process that is apparently sensitized bysunlight. If the source from the snowpack is a largescale feature of the Arctic then the diurnal trendsalso require a competing process for removal to thesurface. From the diurnal change in the NO/NO2ratio, mid-April mixing ratios for the sum of peroxyand halogen oxide radicals of 10 pptv werederived for periods when ozone mixing ratios were inthe normal range of 30–50 ppbv. Mid-day ozoneproduction and loss rates with the active nitrogensource were estimated to be 1–2 ppbv/day and in nearbalance. NOy mixing ratios which averaged only295±66 pptv do not support a large accumulation inthe high Arctic surface layer in the winter and springof 1998. The small abundance of NOy relative tothe elevated mixing ratios of other long-livedanthropogenic constituents requires that reactivenitrogen be removed to the surface during transport toor during residence within the high Arctic.  相似文献   

18.
A seven-year record of surface ozone measurements from Denali NationalPark, Alaska shows a persistent spring maximum. These data, combined withmeasurements of NOx, hydrocarbons, O3, and PANfrom a continental site in Alaska during the spring of 1995 are used as thebasis for a sensitivity study to explore tropospheric photochemistry in thisregion. Because of the relatively high concentrations of NOx(mean of 116, median of 91 pptv), the net tendency was for photochemicalozone production. The range of net O3 production for averageconditions measured at this site during spring is between 0.96–3.9ppbv/day depending on the assumptions used; in any case, this productionmust contribute to the observed springtime maximum in O3.Model calculations showed that of the anthropogenic ozone precursors, onlyNOx had a strong effect on the rate of ozone production; themeasured concentrations of anthropogenic hydrocarbons did not significantlyaffect the ozone budget. Naturally produced biogenic hydrocarbons, such asisoprene, may also have a significant effect on ozone production, even atconcentrations of a few 10's of pptv. An observed temperature-isoprenerelationship from a boreal site in Canada indicates that isoprene may bepresent during the Alaskan spring. Measurements of isoprene taken duringthe spring of 1996 suggest that reactive biogenic hydrocarbon emissionsbegin before the emergence of leaves on deciduous trees and that theconcentrations were sufficient to accelerate ozone production.  相似文献   

19.
Summary Prior to and following the development of a windstorm in the mountainous coastal area of southern Korea, ground level ozone (O3)-concentrations near Kangnung city, on the lee side of the mountains, show a maximum value at approximately 1300 LST, owing to a photolytic cycle of NO2–NO–O3 during the day and a minimum in concentrations at night as a result of the reverse cycle. During the development period of the windstorm, ozone concentrations are generally high all day, and slightly higher during the night. This distribution pattern of ozone is very different from the typical distribution of ozone in the absence of windstorms. High daytime concentrations of ozone during the windstorm are due to both the increase in the amount of ozone from photochemical reactions involving NOx and the increase in O3-concentration due to a decrease in the convective boundary layer thickness under the influence of downslope windstorm conditions on the lee-side of the mountains. At night, the windstorm increases in intensity as the westerly winds combine with a katabatic wind blowing downslope toward the surface at the coast. This causes momentum transport of air parcels in the upper levels toward the surface at the coast and the development of internal gravity waves, which generate a hydraulic jump directed upward over the coast and the East sea, thereby reducing to very thin the thickness of the nocturnal surface inversion layer (NSIL). The higher O3-concentration at night depends mainly upon the shallow NSIL and on some O3 being transported by the momentum transfer from the upper troposphere toward the ground in windstorm conditions.  相似文献   

20.
Formic and acetic acid measured as daily averages in 1993–1994show equal and highly correlated concentrations up to 3 ppb in the summer(May–August). In the winter (October–March) the formicacid/acetic acid ratio was 0.6 and the formic acid concentrations wereusually below 1 ppb. In winter the carboxylic acids correlate withOx, NOy, SO2 and particulatesulphur. The main sources are suggested to be ozonolysis of anthropogenicalkenes and reactions between peroxyacetyl radicals and RO2radicals. In spring–summer the carboxylic acids correlate withO3, Ox, HNO3, PAN,NOy, SO2, particulate sulphur and temperature.In addition to the sources of the winter a contribution from ozonolysis ofbiogenic alkenes is likely. Quite similar formic acid/acetic acid ratios forall wind directions suggest that the source(s) are atmospheric oxidationprocesses distributed over large areas. The highest concentrations occurringfor winds from east to south and the correlation with e.g., particulatesulphur indicate chemical production in polluted air masses during longrange transport.  相似文献   

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