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1.
Geologic seepage of methane and light (C2-C5) alkanes was measured at the La Brea Tar Pits in Los Angeles. Samples were collected using flux chambers with stainless steel canisters and analyzed using gas chromatography. Average seepage rates from individual seepage sites were 970 ± 330 mg/h of methane, 14.0 ± 5.5 mg/h of ethane, 9.1 ± 3.7 mg/h of propane, 3.7 ± 1.6 mg/h of i-butane, 0.33 ± 0.16 mg/h of n-butane, 260 ± 120 μg/h of i-pentane, and 5.3 ± 1.9 μg/h of n-pentane, while maximum seepage rates exceeded 17 g/h of methane, 270 mg/h of ethane, 190 mg/h of propane, 95 mg/h of i-butane, 10 mg/h of n-butane, 7 mg/h of i-pentane, and 0.1 mg/h of n-pentane. These absolute fluxes have an additional unknown amount of error associated with them due to sampling methodology, and should be taken as the lower limit of emissions. Samples collected revealed generally dry gas, with high methane emissions relative to the light alkanes. Overall emissions from the tar pits were found to come not only from the active geologic seepage, but also from the outgassing of the standing asphalt at the site. Using the gas ratios, which are negligibly affected by errors introduced by sampling methodology, observed in this study, daily emissions of C2 – C5 alkanes from the La Brea area were estimated to be 4.7 ± 1.6 Mg, which represents 2–3 % of total emissions in the entire Los Angeles region.  相似文献   

2.
Biogenic Hydrocarbon Chemistry within and Above a Mixed Deciduous Forest   总被引：1，自引：0，他引：1  
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3.
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4.
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5.
C2-C6 Nonmethane hydrocarbon (NMHC) concentrations in the atmospheric boundary layer and in surface seawater were simultaneously measured during an oceanographic cruise in the intertropical Indian Ocean. NMHC were found to be mainly C2-C4 alkenes and C2-C3 alkanes. Their concentrations ranged from 1 to 30×10–9 l/l in the seawater and 0.1 to 15 ppbv in the atmosphere. Seawater appeared to be a source because the C2-C6 NMHC were supersaturated with respect to the atmosphere by 2 or 3 orders of magnitude.After a selection of the pure marine atmospheric samples, performed with the help of stable and radioactive continental tracers, we found an identical composition in NMHC of surface air and seawater. This observation enabled us to establish that the gas transfer between sea and air occurred according to nonsteady state processes, and that the fluxes cannot be deduced only from atmospheric measurements. An order of magnitude value of the oceanic source for the different NMHC is however derived from the comparison of their sea water concentrations to that of propane and an independent evluation of the marine source of this last compound.  相似文献   

6.
城市低层大气臭氧生成的模拟研究   总被引：7，自引：0，他引：7  
蒋维楣  李昕等 《气象科学》2001,21(2):154-161
利用一个城市边界层臭氧模式，以南京市为对象，研究了臭氧在城市低层大气中的形成机制和规律，得出了南京市18个交通点的日臭氧浓度最大值的分布图。结果表明，南京市白天有相当长的时间是处于臭氧超标的状态，不少交通点的日最大臭氧浓度值是标准的2－3倍。文章还模拟了PAN，OH自由基和HCHO这三种重要物种的日变化规律。同时，本文选择南京市东郊的紫金山风景区，实次探讨了植物排放有机物对臭氧生成的贡献。从模式的模拟研究可得，与人为因素相比，植物排放对臭氧生成的作用也是不可忽视的，值得作深入一步的探讨。  相似文献   

7.
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   

8.
Three online coupled chemical transport model simulations were analyzed for three summer months of 2015 in Poland. One of them was run with default emission inventory, the other two with NOx and VOC emissions reduced by 30%, respectively. Obtained ozone concentrations were evaluated with data from air quality measurement stations and ozone sensitivity to precursor emissions was estimated by ozone concentration differences between simulations and with the use of indicator ratios. They were calculated based on modeled mixing ratios of ozone, total reactive nitrogen and its components, nitric acid and hydrogen peroxide. The results show that the model overestimates ozone concentrations with the largest errors in the morning and evening, which is primarily related to the way vertical mixing is resolved by the model. Better model performance for ozone is achieved in rural than urban environment, as PBL and mixing mechanisms play more significant role in urban areas. Modeled ozone shows mixed sensitivity to precursor concentrations, similarly to other European regions, but indicator ratios have different values than are found in literature, particularly H2O2/HNO3 is larger than in southern Europe. However, indicator ratios often differ between locations and transition values need to be established individually for a given region.  相似文献   

9.
The objectives of this study were to identify species and levels of volatile organic compounds (VOCs), and determine their oxidation capacity in the rural atmosphere of western Senegal. A field study was conducted to obtain air samples during September 14 and September 15, 2006 for analyses of VOCs. Methanol, acetone, and acetaldehyde were the most abundant detected chemical species and their maximum mixing ratios reached 6 parts per billion on a volume basis (ppbv). Local emission sources such as firewood and charcoal burning strongly influenced VOC concentrations. The VOC concentrations exhibited little temporal variations due to the low reactivity with hydroxyl radicals, with reactivity values ranging from 0.001 to 2.6 s−1. The conditions in this rural site were rather clean. Low ambient NO x levels limited ozone production. Nitrogen oxide (NO x ) levels reached values less than 2 ppbv and maximum VOC/NO x ratios reached 60 ppbvC/ppbv, with an overall average of 2.4 ± 4.5 ppbvC/ppbv. This indicates that the rural western Senegal region is NO x limited in terms of oxidant formation potential. Therefore, during the study period photochemical ozone production became limited due to low ambient NO x levels. The estimated ozone formation reactivity for VOCs was low and ranged between −5.5 mol of ozone/mol of benzaldehyde to 0.6 mol/mol of anthropogenic dienes.  相似文献   

10.
Summary The CIT photochemical model was used to investigate the effectiveness of ozone control strategies for Athens, Greece. A unique aspect of this study was the use of two different wind fields, one from a prognostic model, and the other derived with objective analysis procedures. This allows investigating to what degree the wind fields both derived using accepted methods, influence control strategy evaluation. Strategies investigated included reducing ROG and NO x , and combinations of the two. For the period studied, the use of different meteorological field preparation techniques did not influence the direction of the ozone response to controls. In both cases (i.e. using prognostic or objective analysis wind fields), reducing NO x led to predicted increases in ozone levels at the measurement stations, and ROG control lowered ozone. PAN concentrations respond similarly to ozone. However, use of the two different wind fields significantly impacted the degree and spatial locations of the responses. Use of the objective analysis fields showed greater response to emission controls because of the lower wind velocities generated. The influence of the biogenic emissions were found to be small. Also, a number of key data necessary for future studies of this kind were identified, as well as modeling domain questions.With 14 Figures  相似文献   

11.
To systematically explain relations between light hydrocarbons, CO, and CO2 concentrations/emissions of biomassburning, we measured concentrations/emissions of carbon gases – CO,CO2, light hydrocarbons (CH4, C2H6,C2H4, C2H2, C3H8, C3H6,n-C4H10, i-C4H10, n-C5H12,i-C5H12), and THC (total hydrocarbon) – in the burning of dead plant material, mainly Imperata grass, byclosed-chamber experiments and by time-series analyses of gas concentrations in combustion plumes in relatively efficient and inefficient combustion situations. Concentrations of hydrocarbons measured were well correlated to [CO] although [C2H2] was exceptionally well correlated to[CO2]. The phase diagrams (relation between [CO]/ [CO2] and [hydrocarbon]/ [CO2]) obtained by the time-seriesexperiments well illustrated the variation in the overall emission rates of the closed-chamber experiments. The higher rates of decrease in hydrocarbon concentration with increasing carbon number in the efficient case compared with the inefficient case probably reflected the rate of oxidation and the amount of radicals. The overall concentrations (or emissions) of C2H4 and C3H6 were higher thanthose of C2H6 and C3H8, suggesting a linkage to mechanisms in whichthe predominant path of hydrocarbon oxidation is through the degradation of alkyl radicals, which can be immediately converted into or formed from alkenes. For C3 and C4 species, normal-chain species hadhigher emissions than iso-chain species under lower combustion efficiency. This may be attributable to the presence of tertiary C–H bonds in iso-species,which show more reactivity in the abstraction of H than secondary C–H bonds unless the carbon number is large.  相似文献   

12.
We present a comprehensive discussion on what cause high ozone episodes at a suburban photochemical observation site of the Seoul Metropolitan Area (population ～23 million). The observational site, Taehwa Research Forest (TRF), is situated ～30 km from the center of Seoul. In June 2011, we observed two very distinctive ozone periods-high ozone (peak up to 120 ppbv) and low ozone (peak up to 60 ppbv) in the mid and early month, respectively. The trace gas measurement dataset, especially CO and NO X clearly indicate that less anthropogenic influences during the high ozone period. Volatile organic compound (VOC) measurement results show that at the observational site, biogenic VOCs (mostly isoprene) contribute most of chemical reactivity towards OH, although toluene from anthropogenic activities was observed in higher concentrations. Back-trajectory analysis indicates that air-masses from the forest part of Korea Peninsula were dominant influences during the high ozone episode event. On the other hand, Aged air masses from China were the dominant influence during the low ozone episode event. Model calculations conducted using the University of Washington Chemical Mechanism (UWCM) box model, also consistently show that BVOC, especially isoprene photochemistry, can be the significantly contribution to local ozone formation in the given photochemical environments of TRF. These research results strongly suggest that ozone control strategy in the Eastern Asian megacities, mostly situated in surrounding forest areas should be based on the comprehensive scientific understanding in BVOC photochemistry and interplays between anthropogenic and biogenic interactions.  相似文献   

13.
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   

14.
Ozone Concentrations in Rural Regions of the Yangtze Delta in China   总被引：4，自引：0，他引：4  
Elevated concentrations of ozone have been observed at six non-urban, surface monitoring sites in the Yangtze Delta of China during a 16-month field experiment carried out in 1999 and 2000 as part of the joint Chinese-American China-MAP Project (the Yangtze Delta of china as an Evolving Metro-Agro-Plex). The average daytime (0900–1600 h) ozone levels for the monitoring period at sites ranged from 35 to 47 ppbv (parts per billion by volume) and the mean ozone levels from 26 to 35 ppbv. Observed data show seasonal variation obviously, with highest mixing ratios of ozone in May. Average daytime ozone levels in May at sites were between 60 and 79 ppbv. High ozone concentrations were most prevalent during the late spring. Frequency counts of hourly mean ozone concentration over 60 ppbv and 40 ppbv appeared peak values of 22–39% and 42–74% in May at sites. Even higher daytime ozone levels were observed during two regional episodes, in which average daytime (0900–1600 h) ozone concentrations during 10 May and 23 May 2000 were 68 to 81 ppbv, during Oct. 18 and Oct. 28, 1999 were 59 to 67 ppbv at sites. Peak value of ozone mixing ratio appearing in late spring, instead of in summer, was attributed to summer monsoon. Backward trajectories showed that ozone episodes associated with meteorological conditions. Also many high ozone levels associated with high CO levels and high CO to NO x ratios, which suggests a contribution from sources of emission involving incomplete combustion.  相似文献   

15.
Information from a variety of sources, including an airborne field expedition in November 1985, is used to produce estimates of the annual emissions of some hydrocarbons from bushfires, and isoprene from trees, in tropical Australia. For the continent north of 23° S the annual bushfires (biomass burning) input was estimated, in units of Tg carbon, to be 2 TgC (uncertainty range 0.8–5 TgC), emitted predominantly during the May to October dryseason. Isoprene emissions during this period were estimated also to be 2 TgC (uncertainty range 0.5–8 TgC), but were estimated to be an order of magnitude higher during the November to April wet season, at a level of 23 TgC (uncertainty range 6–100 TgC).The large annual emission of isoprene over the tropical part of the Australian continent yields ppbv levels of isoprene measured at the surface in summertime. Isoprene reactivity with hydroxyl radical is such that at these concentrations isoprene must be a dominant factor in controlling the concentration of OH radical in the convective boundary layer. Simple arguments based on the convective velocity scale suggest that the shape of the isoprene vertical profile in November 1985 would be consistent with available data on the OH-isoprene reaction rate if OH concentration in the boundary layer averaged about 2.5×106 cm-3 over the middle part of the day.Temporarily at the International Meteorological Institute, Stockholm University, S-106 91, Stockholm, Sweden.  相似文献   

16.
A one-dimensional coupled climate and chemistry model has been developed to estimate past and possible future changes in atmospheric temperatures and chemical composition due to human activities. The model takes into account heat flux into the oceans and uses a new tropospheric temperature lapse rate formulation. As found in other studies, we estimate that the combined greenhouse effect of CH4, O3, CF2Cl2, CFCl3 and N2O in the future will be about as large as that of CO2. Our model calculates an increase in average global surface temperatures by about 0.6°C since the start of the industrial era and predicts for A.D. 2050 a twice as large additional rise. Substantial depletions of ozone in the upper stratosphere by between 25% and 55% are calculated, depending on scenario. Accompanying temperature changes are between 15°C and 25°C. Bromine compounds are found to be important, if no rigid international regulations on CFC emissions are effective. Our model may, however, concivably underestimate possible effects of CFCl3, CF2Cl2, C2F3Cl3 and other CFC and organic bromine emissions on lower stratospheric ozone, because it can not simulate the rapid breakdown of ozone which is now being observed worldwide. An uncertainty study regarding the photochemistry of stratospheric ozone, especially in the region below about 25 km, is included. We propose a reaction, involving excited molecular oxygen formation from ozone photolysis, as a possible solution to the problem of ozone concentrations calculated to be too low above 45 km. We also estimate that tropospheric ozone concentrations have grown strongly in the northern hemisphere since pre-industrial times and that further large increases may take place, especially if global emissions of NOx from fossil fuel and biomass burning were to continue to increase. Growing NOx emissions from aircraft may play an important role in ozone concentrations in the upper troposphere and low stratosphere.  相似文献   

17.
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   

18.
The seasonal and diurnal variations of ozone mixing ratios have been observed at Niwot Ridge. Colorado. The ozone mixing ratios have been correlated with the NO x (NO+NO2) mixing ratios measured concurrently at the site. The seasonal and diurnal variations in O3 can be reasonably well understood by considering photochemistry and transport. In the winter there is no apparent systematic diurnal variation in the O3 mixing ratio because there is little diurnal change of transport and a slow photochemistry. In the summer, the O3 levels at the site are suppressed at night due to the presence of a nocturnal inversion layer that isolated ozone near the surface, where it is destroyed. Ozone is observed to increase in the summer during the day. The increases in ozone correlate with increasing NO x levels, as well as with the levels of other compounds of anthropogenic origin. We interpret this correlation as in-situ or in-transit photochemical production of ozone from these precursors that are transported to our site. The levels of ozone recorded approach 100 ppbv at NO x mixing ratios of approximately 3 ppbv. Calculations made using a simple clean tropospheric chemical model are consistent with the NO x -related trend observed for the daytime ozone mixing ratio. However, the chemistry, which does not include nonmethane hydrocarbon photochemistry, underestimates the observed O3 production.  相似文献   

19.
A comparison of the atmospheric chemistry mechanisms EMEP (Co-operative Programme for Monitoring and Evaluation of the Long-Range Transmission of Air Pollutants in Europe), RADM2 (Regional Acid Deposition Model, version 2) and RACM (Regional Atmospheric Chemistry Mechanism) has been conducted. Each mechanism was used to simulate the PLUME case of Kuhn et al. (1998) and to simulate an additional 150 and 81 scenarios with and without emissions, respectively. These simulations covered scenarios that ranged from relatively clean, through rural and polluted urban conditions. Ozone isopleths and scatter plots were generated from the simulations. The mechanisms were compared primarily on the basis of calculated ozone and ozone precursor concentrations. For the gas-phase ozone precursors the differences between the mechanisms were rather small under clean conditions and more significant under polluted conditions. The differences were especially significant for the concentrations of NO2 and organic peroxy radicals. In general the EMEP mechanism yielded the most ozone and the RADM2 mechanism yielded the least. Furthermore the results suggest that a broad range simulation conditions should be used to compare mechanisms and not just a few selected scenarios.  相似文献   

20.
During the BERLIOZ field phase on 20 July 1998 a 40 km wide ozone-plume 30 to 70 km north of Berlin in the lee of the city was detected. The ozone mixing ratio inside the plume was app. 15 ppb higher than outside, mainly caused by high ozone precursor emissions in Berlin, resulting in a net chemical ozone production of 6.5 ppb h–1, which overcompensates ozone advection of –3.6 ppb h–1 andturbulent diffusion of –1.1 ppb h–1. That means, although moreozone leaves the control volume far in the lee of Berlin than enters it at the leeside cityborder and although turbulent diffusion causes a loss of ozone in the leeside control volume the chemical production inside the volume leads to a net ozone increase. Using a semi-Lagrangian mass budget method to estimate the net ozone production, 5.0 ppb h–1 are calculated for theplume. This means a fraction of about 20% of ozone in the plume is producedby local emissions, therefore called `home made' by the Berlin emissions. For the same area KAMM/DRAIS simulations using an observation based initialisation, results in a net production rate between 4.0 and 6.5 ppbh–1, while the threefold nested EURAD model gives 6.0 ppbh–1. The process analysis indicates in many cases goodagreement (10% or better) between measurements and simulations not only in the ozone concentrations but also with respect to the physical and chemical processes governing the total change. Remaining differences are caused by different resolution in time and space of the models and measurements as well as by errors in the emission calculation.The upwind-downwind differences in PAN concentrations are partly similar to those of ozone, because in the BERLIOZ case they are governed mainly by photochemical production. While in the stable boundary layer at night and windward of Berlin 0.1 to 0.3 ppb are detected, in the centre of the plume at noon concentrations between 0.75 ppb and 1.0 ppb are measured. The O3/PAN ratio is about 80 to 120 and thus due to the relatively lowPAN concentrations significantly higher than found in previous studies. The low PAN formation on 20 July, was mainly restricted by the moderate nonmethane hydrocarbon levels, whereas high PAN concentrations of 3.0 ppb on 21 July, are caused by local production in the boundary layer and by large scale advection aloft.  相似文献   

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