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1.
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2.
Photochemical smog characterized by high concentrations of ozone (O3) is a serious air pollution issue in the North China Plain (NCP) region, especially in summer and autumn. For this study, measurements of O3, nitrogen oxides (NOx), volatile organic compounds (VOCs), carbon monoxide (CO), nitrous acid (HONO), and a number of key physical parameters were taken at a suburban site, Xianghe, in the NCP region during the summer of 2018 in order to better understand the photochemical processes leading to O3 formation and find an optimal way to control O3 pollution. Here, the radical chemistry and O3 photochemical budget based on measurement data from 1-23 July using a chemical box model is investigated. The daytime (0600-1800 LST) average production rate of the primary radicals referred to as ROx (OH + HO2+ RO2) is 3.9 ppbv h-1. HONO photolysis is the largest primary ROx source (41％). Reaction of NO2 + OH is the largest contributor to radical termination (41％), followed by reactions of RO2 + NO2 (26％). The average diurnal maximum O3 production and loss rates are 32.9 ppbv h-1 and 4.3 ppbv h-1, respectively. Sensitivity tests without the HONO constraint lead to decreases in daytime average primary ROx production by 55％ and O3 photochemical production by 42％, highlighting the importance of accurate HONO measurements when quantifying the ROx budget and O3 photochemical production. Considering heterogeneous reactions of trace gases and radicals on aerosols, aerosol uptake of HO2 contributes 11％ to ROx sink, and the daytime average O3 photochemical production decreases by 14％. The O3-NOx-VOCs sensitivity shows that the O3 production at Xianghe during the investigation period is mainly controlled by VOCs.  相似文献   

3.
Summer and winter campaigns for the chemical compositions and sources of nonmethane hydrocarbons(NMHCs)and oxygenated volatile organic compounds(OVOCs)were conducted in Xi’an.Data from 57 photochemical assessment monitoring stations for NMHCs and 20 OVOC species were analyzed.Significant seasonal differences were noted for total VOC(TVOC,NMHCs and OVOCs)concentrations and compositions.The campaign-average TVOC concentrations in winter(85.3±60.6 ppbv)were almost twice those in summer(47.2±31.6 ppbv).Alkanes and OVOCs were the most abundant category in winter and summer,respectively.NMHCs,but not OVOCs,had significantly higher levels on weekends than on weekdays.Total ozone formation potential was higher in summer than in winter(by 50%)because of the high concentrations of alkenes(particularly isoprene),high temperature,and high solar radiation levels in summer.The Hybrid Environmental Receptor Model(HERM)was used to conduct source apportionment for atmospheric TVOCs in winter and summer,with excellent accuracy.HERM demonstrated its suitability in a situation where only partial source profile data were available.The HERM results indicated significantly different seasonal source contributions to TVOCs in Xi’an.In particular,coal and biomass burning had contributions greater than half in winter(53.4%),whereas traffic sources were prevalent in summer(53.1%).This study’s results highlight the need for targeted and adjustable VOC control measures that account for seasonal differences in Xi’an;such measures should target not only the severe problem with VOC pollution but also the problem of consequent secondary pollution(e.g.,from ozone and secondary organic aerosols).  相似文献   

4.
The intensive field study POPCORN (Photo-Oxidant Formation by Plant Emitted Compounds and OH Radicals in North-Eastern Germany) was carried out in a rural area of North-Eastern Germany during August 1994. An overview of the objectives, measurements and major results of this campaign is presented. Measurements of a set of relevant atmospheric trace compounds, including the hydroxyl radical, along with meteorological data were performed to increase the understanding of OH radical chemistry and photo-oxidant formation. Additionally, plant emissions and the exchange of trace gases between a maize field and the atmosphere were investigated. Budgets of selected trace gases were calculated to assess the relative importance of local sources, chemistry or transport. Intercomparisons between measurement techniques were a central issue of POPCORN and included measurements of OH, hydrocarbons, formaldehyde, photolysis frequencies and vertical fluxes. OH radical concentrations were measured simultaneously by LIF (Laser Induced Fluorescence) and DOAS (Differential Optical Absorption Spectroscopy). Both methods showed good agreement. Maximum OH concentrations were around 107 cm–3 and the diurnal cycles closely followed the rate of primary production via ozone photolysis. Generally, the trace gas composition during POPCORN was characterized by relatively low concentrations of most compounds, e.g. CO: 85–200 ppb, ethane: 0.6–2 ppb, and moderate NOx levels: 0.5–5 ppb (at noontime). Concentrations of individual biogenic volatile organic compounds (VOC) were mostly well below 100 ppt. However, formaldehyde and acetaldehyde which partly originate from biological sources were observed at mixing ratios of some ppb.  相似文献   

5.
Particulate matter with diameters of 2.5 μm or smaller(PM_(2.5)) and ozone(O_3) are major pollutants in the urban atmosphere. PM_(2.5) can affect O_3 by altering the photolysis rate and heterogeneous reactions. However, these two processes and their relative importance remain uncertain. In this paper, with Nanjing in China as the target city, we investigate the characteristics and mechanism of interactions between particles and O_3 based on ground observations and numerical modeling.In 2008, the average concentrations of PM_(2.5) and O_3 at Caochangmen station are 64.6 ± 47.4 μg m~(-3) and 24.6 ± 22.8 ppb,respectively, while at Pukou station they are 94.1 ± 63.4 μg m~(-3) and 16.9 ± 14.9 ppb. The correlation coefficient between PM_(2.5) and O_3 is -0.46. In order to understand the reaction between PM_(2.5) and O_3, we construct a box model, in which an aerosol optical property model, ultraviolet radiation model, gas phase chemistry model, and heterogeneous chemistry model,are coupled. The model is employed to investigate the relative contribution of the aforementioned two processes, which vary under different particle concentrations, scattering capability and VOCs/NOxratios(VOCs: volatile organic compounds;NOx: nitric oxide and nitrogen dioxide). Generally, photolysis rate effect can cause a greater O_3 reduction when the particle concentrations are higher, while heterogeneous reactions dominate O_3 reduction with low-level particle concentrations.Moreover, in typical VOC-sensitive regions, O_3 can even be increased by heterogeneous reactions. In Nanjing, both processes lead to O_3 reduction, and photolysis rate effect is dominant. Our study underscores the importance of photolysis rate effect and heterogeneous reactions for O_3, and such interaction processes should be fully considered in future atmospheric chemistry modeling.  相似文献   

6.
Black carbon(BC) reduces the photolysis coefficient by absorbing solar radiation, thereby affecting the concentration of ozone(O_3) near the ground. The influence of BC on O_3 has thus received much attention. In this study, Mie scattering and the tropospheric Ultraviolet and Visible radiation model are used to analyze the effect of BC optical properties on radiation. Combined with data of O_3 precursors in Nanjing in 2014, an EKMA curve is drawn, and the variations in O_3 concentration are further investigated using a zero-dimensional box mechanism model(NCAR MM). When O_3 precursors are unchanged, radiation and O_3 show a highly similar tendency in response to changing BC optical properties(R=0.997).With the increase of modal radius, the attenuation of fresh BC to radiation and O_3 first trends upward before decreasing. In the mixing process, the attenuation of BC to radiation and O_3 presents an upward tendency with the increase of relative humidity but decreases rapidly before increasing slowly with increasing thickness of coating. In addition, mass concentration is another major factor. When the BC to PM2.5 ratio increases to 5% in Nanjing, the radiation decreases by approximately 0.13%–3.71% while O_3 decreases by approximately 8.13%–13.11%. The radiative effect of BC not only reduces O_3 concentration but also changes the EKMA curve. Compared with the NOx control area, radiation has a significant influence on the VOCs control area. When aerosol optical depth(AOD) increases by 17.15%, the NOx to VOCs ratio decreases by 8.27%, and part of the original NOx control area is transferred to the VOCs control area.  相似文献   

7.
The representation of alkene degradation in version 3 of the Master Chemical Mechanism (MCM v3) has been evaluated, using environmental chamber data on the photo-oxidation of ethene, propene, 1-butene and 1-hexene in the presence of NOx, from up to five chambers at the Statewide Air Pollution Research Center (SAPRC) at the University of California. As part of this evaluation, it was necessary to include a representation of the reactions of the alkenes with O(3P), which are significant under chamber conditions but generally insignificant under atmospheric conditions. The simulations for the ethene and propene systems, in particular, were found to be sensitive to the branching ratios assigned to molecular and free radical forming pathways of the O(3P) reactions, with the extent of radical formation required for proper fitting of the model to the chamber data being substantially lower than the reported consensus. With this constraint, the MCM v3 mechanisms for ethene and propene generally performed well. The sensitivity of the simulations to the parameters applied to a series of other radical sources and sink reactions (radical formation from the alkene ozonolysis reactions and product carbonyl photolysis; radical removal from the reaction of OH with NO2 and β-hydroxynitrate formation) were also considered, and the implications of these results are discussed. Evaluation of the MCM v3 1-butene and 1-hexene degradation mechanisms, using a more limited dataset from only one chamber, was found to be inconclusive. The results of sensitivity studies demonstrate that it is impossible to reconcile the simulated and observed formation of ozone in these systems for ranges of parameter values which can currently be justified on the basis of the literature. As a result of this work, gaps and uncertainties in the kinetic, mechanistic and chamber database are identified and discussed, in relation to both tropospheric chemistry and chemistry important under chamber conditions which may compromise the evaluation procedure, and recommendations are made for future experimental studies. Throughout the study, the performance of the MCM v3 chemistry was also simultaneously compared with that of the corresponding chemistry in the SAPRC-99 mechanism, which was developed and optimized in conjunction with the chamber datasets.  相似文献   

8.
Recently, the China Meteorological Administration (CMA) released a new Global Atmospheric Reanalysis (CRA-40) dataset for the period 1979-2018. In this study, surface relative humidity (RH) from CRA-40 and other current reanalyses (e.g., CFSR, ERA5, ERA-Interim, JRA-55, and MERRA-2) is comprehensively evaluated against homogenized observations over China. The results suggest that most reanalyses overestimate the observations by 15％-30％ (absolute difference) over the Tibetan Plateau but underestimate the observations by 5％-10％ over most of northern China. The CRA-40 performs relatively well in describing the long-term change and variance seen in the observed surface RH over China. Most of the reanalyses reproduce the observed surface RH climatology and interannual variations well, while few reanalyses can capture the observed long-term RH trends over China. Among these reanalyses, the CFSR does poorly in describing the interannual changes in the observed RH, especially in Southwest China. An empirical orthogonal function (EOF) analysis also suggests that the CRA-40 performs better than other reanalyses to capture the first two leading EOF modes revealed by the observations. The results of this study are expected to improve understanding of the strengths and weaknesses of the current reanalysis products and thus facilitate their application.  相似文献   

9.
大气CO2浓度增加,大气辐射平衡调整,将影响到大气的辐射加热,对季风环流的产生影响.CMIP6结果显示,大气CO2浓度增加,可减弱季风区主雨季对流层高,低层的辐射加热,加强对流层中层的辐射加热.各季风区加热响应的峰值层次不同:亚洲季风区平均层次最高(500-775 hPa),北非,南美,澳洲季风区次之(550-600 hPa),北美(600hPa)和南非季风区(600-775 hPa)较低.各季风区水云的垂直分布及其长波辐射效应的变化是形成峰值层次差异的主因.  相似文献   

10.
This study uses the WRF-Chem model combined with the empirical kinetic modeling method (EKMA curve) to study the compound pollution event in Beijing that happened in 13-23 May 2017. Sensitivity tests are conducted to analyze ozone sensitivity to its precursors, and to develop emission reduction measures. The results suggest that the model can accurately simulate the compound pollution process of photochemistry and haze. When VOCs and NOx were reduced by the same proportion, the effect of O3 reduction at peak time was more obvious, and the effect during daytime was more significant than at night. The degree of change in ozone was peak time > daytime average. When reducing or increasing the ratio of precursors by 25％ at the same time, the effect of reducing 25％ VOCs on the average ozone concentration reduction was most significant. The degree of change in ozone decreased with increasing altitude, the location of the ozone maximum change shifted westward, and its range narrowed. As the altitude increases, the VOCs-limited zone decreases, VOCs sensitivity decreases, NOx sensitivity increases. The controlled area changed from near-surface VOCs-limited to high-altitude NOx-limited. Upon examining the EKMA curve, we have found that suburban and urban are sensitive to VOCs. The sensitivity tests indicate that when VOCs in suburban are reduced about 60％, the O3-1h concentration could reach the standard, and when VOCs of the urban decreased by about 50％, the O3-1h concentration could reach the standard. Thus, these findings could provide references for the control of compound air pollution in Beijing.  相似文献   

11.
A high-sensitive technique to detect O(1S) atoms using vacuum ultraviolet laser-induced fluorescence (VUV-LIF) spectroscopy has been applied to study the O(1S) production process from the UV photodissociation of O3, N2O, and H2O2. The quantum yields for O(1S) formation from O3 photolysis at 215 and 220 nm are determined to be (1.4 ± 0.4) × 10−4 and (5 ± 3) × 10−5, respectively. Based on thermochemical considerations, the O(1S) formation from O3 photolysis at 215 and 220 nm is attributed to a spin-forbidden process of O(1S)+O2(X3Σg −). Analysis of the Doppler profile of O(1S) produced from O3 photolysis at 193 nm also indicates that the O(1S) atoms are produced from the spin-forbidden process. In the photolysis of N2O and H2O2 at 193 nm, no discernible signal of O(1S) atoms has been detected. The upper limit values of the quantum yields for O(1S) production from N2O and H2O2 photolysis at 193 nm are estimated to be 8 × 10−5 and 3 × 10−5, respectively. Using the experimental results, the impact of the O(1S) formation from O3 photolysis on the atmospheric OH radical formation through the reaction of O(1S)+H2O has been estimated. The calculated results show that the contribution of the O(1S)+H2O reaction to the OH production rate is ∼2% of that of the O(1D)+H2O reaction at 30 km altitude in mid-latitude. Implications of the present laboratory experimental results for the terrestrial airglow of O(1S) at 557.7 nm have also been discussed.  相似文献   

12.
为研究雾和霾天气下VOCs时空变化特征,于2020年11月19 日—2021年1月15日在江苏省东海国家气象观测站进行为期58 d的外场观测试验。利用自主研发的多旋翼无人机捕获2次辐射雾和2次霾天气过程,获得气温、气压、相对湿度、风向、风速、VOCs、O3等7种要素100多条垂直廓线。结果表明:时间上,霾过程夜间VOCs体积浓度(0.225~0.253 ppm(parts per million, 1 ppm=10-6))明显高于白天(0.191~0.205 ppm),雾形成前体积浓度(0.121~0.239 ppm)显著高于雾过程(0.056~0.209 ppm)。雾过程中VOCs体积浓度与雾强度变化相反,雾层高度与VOCs体积浓度剧烈变化高度一致,雾层(<200 m)中VOCs体积浓度(0.172~0.178 ppm)明显减小,显著低于雾形成前(0.195~0.240 ppm),雾层以上浓度变化大,雾结束后1 h内保持雾过程中分布特点。雾对逆温层中的水溶性污染物有清除作用,VOCs体积浓度和O3质量浓度均下降。  相似文献   

13.
基于2015-2020年北京35个环境空气站和20个气象站观测资料,应用机器学习方法(随机森林算法)分离了气象条件和源排放对大气污染物浓度的影响.结果发现,为应对疫情采取的隔离措施使北京2020年春节期间大气污染物浓度降低了35.1％-51.8％;其中,背景站氮氧化物和一氧化碳浓度的降幅最大,超过了以往报道较多的交通站点.同时,2020年春节期间的气象条件不利于污染物扩散,导致多次霾污染事件发生.为进一步改善北京空气质量,未来需要优化减排策略.  相似文献   

14.
Using long path UV absorption spectroscopy we have measured OH concentrations close to the earth's surface. The OH values observed at two locations in Germany during 1980 through 1983 range from 0.7×106 to 3.2×106 cm-3. Simultaneously we measured the concentrations of O3, H2O, NO, NO2, CH4, CO, and the light non methane hydrocarbons. We also determined the photolysis rates of O3 and NO2. This allows calculations of OH using a zero dimensional time depdendent model. The modelled OH concentrations significantly exceed the measured values for low NO x concentrations. It is argued that additional, so far unidentified. HO x loss reactions must be responsible for that discrepancy.  相似文献   

15.
Isoprene peroxy radical isomerizations (1,5- and 1,6-H shifts) have recently been proposed as important pathways regenerating and recycling HOx (OH?+?HO2) in the atmosphere under low-NOx conditions (Peeters et al. Phys. Chem. Chem. Phys. 28: 5935?C5939 2009; da Silva et al. Environ. Sci. Technol. 44:250?C256 2010). Evaluation and comparison of the isoprene peroxy radical isomerization mechanisms from recent studies have been performed against isoprene-NOx experiments conducted in the UNC dual outdoor smog chambers. Five different kinetic mechanisms were tested in this study, including the original Master Chemical Mechanism (MCM) v3.1; two modified MCM mechanisms both implementing isoprene peroxy radical isomerization reactions but with different rate coefficients; the Carbon Bond 6 (CB6) mechanism; and the ISO-UNC mechanism. Sensitivity analyses of the unsaturated hydroxyperoxy aldehydes (HPALDs) reaction mechanisms under fast isomerization have also been performed. The results indicate that the fast isomerization mechanism and the mechanisms with high OH yields from HPALDs photolysis both significantly enhance HOx estimates with increasing isoprene/NOx ratios. However, O3 predictions, as well the isoprene decay rates are substantially overestimated. Our results suggest that given the current state of our knowledge, it is difficult to improve both HOx levels and maintain reasonable O3 simulations using the Peeters et al. (Peeters et al. Phys. Chem. Chem. Phys. 28: 5935?C5939 2009) mechanism.  相似文献   

16.
To investigate the impacts of relative humidity(RH) on secondary organic aerosol(SOA) concentrations and chemical reactions, the carbonaceous aerosol components [i.e., organic carbon(OC) and element carbon(EC)] were quantified in daily PM2.5 samples collected at a background site in East China during summer 2015. Based on the method of EC-tracer, the concentration of secondary organic carbon(SOC) demonstrated an obvious negative relationship with RH higher than 60%. Moreover, the ratio of SOC/EC also exhibited obvious decreasing trends with increasing RH, indicating negative effects for chemical production of SOA under high RH conditions. Due to high RH,photochemistry was weakened, gaseous oxidant concentrations was lowered(e.g., significantly decreased O3 levels),and the production rates of SOA were relatively low. On the other hand, because of more water uptake under higher RH conditions, the aerosol droplet acidity was reduced and enhancement of SOA formation by acidity was accordingly absent. In addition, high RH also plays an important role in changing viscosity of pre-existing aerosol coatings,which can affect reactive uptake yield of SOA. Overall, the results from this study imply that SOA production may be more associated with photochemical processes, while aqueous-phase chemistry is not very important for some SOA formation in a moist ambient environment. In the ambient atmosphere, oxidant concentrations, reaction rates,airborne species, etc., are highly variable. How do these factors affect SOA yields under given ambient environment warrants further detailed investigations.  相似文献   

17.
Atmospheric concentrations of ca. 250 C6–C15 hydrocarb on and C4–C12 oxygenated volatile organic compounds (VOC) including alkanes, benzene and alkyl benzenes, monoterpenes and aldehydes were measured in August 1994 during the POPCORN campaign (POPCORN = Photo-Oxidant formation by Plant emitted Compounds and OH Radicals in North-Eastern Germany). About 80 substances together contributed 90% of the atmospheric carbon in this range of molecular weight. During this field campaign VOC-emissions from several crop and tree species and the ambient concentrations of CO, C2–C7 non-methane hydrocarbons (NMHC), C1 and C2 aldehydes, nitrogen oxides, ozone and hydroxyl-radicals (OH) were also measured. These data were used to interpret the VOC measurements presented here. The on-line GC–MS used for the VOC measurements combines adsorptive sampling with thermal desorption and GC–MS analysis in an automated system. Internal standards were used to quantify the measurements. Ozone was destroyed prior to the sample preconcentration through the gas phase reaction with NO. Aromatic compounds like benzene, toluene and xylenes were the most abundant compound class among the measured substances, -pinene and 3-carene, most probably originating from pineforests ca. 1 km away from the measuring site, were the most abundant monoterpenes. The highest mixing ratios of most compounds were measured in nights with strong inversion situations. The toluene mixing ratios then reached 630 pptv; -pinene mixing ratios went up to 430 pptv. The median of all toluene and -pinene measurements during the campaign was 125 pptv or 22 pptv, respectively. These values are on the lower end of ambient measurements reported for continental sites. In most samples also n-pentanal, n-hexananl, n-nonanal and n-undecanal were present. Median mixing ratios were 9, 16, 14 and 8 pptv, respectively. Emission studies indicate that these highly reactive compounds are most probably emitted from maize. It is shown by a simple first order approach that the potential for ozone formation during the POPCORN campaign was roughly equal for anthropogenic and biogenic VOC. From measured concentrations of ozone, OH-radicals, methane, CO, C2–C15 nonmethane hydrocarbons (NMHC) and C5–C11 aldehydes a photochemical production of ozone in the order of 3.5 ppb/h can be estimated. Apart from formaldehyde and acetaldehyde, which are at least partly products of VOC oxidation, the substance group with the largest contribution to the VOC turnover are the monoterpenes. They contribute ca. 30%. However, the mechanism of terpene oxidation is very complex and presently only partly understood. Thus the actual contribution of monoterpenes to ozone formation is very uncertain. Other measured compound classes such as light alkenes, alkanes, aromatics, and C5–C11 aldehydes contribute each between 10% and 15% to ozone formation. The measuring site was not influenced directly from strong biogenic or anthropogenic sources, and the results obtained during the POPCORN campaign can be regarded as a typical picture of a remote rural central European environment.  相似文献   

18.
北京雾、霾天细粒子质量浓度垂直梯度变化的观测   总被引：9，自引：3，他引：6  
近年来北京城市区域雾霾天气显著增加,不仅严重影响工农业生产和交通运输,还严重影响人体健康.2007年夏秋季节,北京325 m气象塔8、80和240m平台梯度观测结果表明,雾、霾、晴三种典型天气状况大气细粒子质量浓度垂直分布各有特点,雾天(11月5～6日)低层浓度明显偏高,6日从低到高3层PM2.5(空气动力学直径小于等于2.5μ的大气气溶胶)浓度日均值分别为352.6±79.3、224.7±69.0、214.8±32.8 μg·m~(-3);霾天(8月19～20日)细粒子上下混合均匀,19日从低到高3层PM2.5浓度分别为89.8±29.3、88.9±29.8、90.0±31.7 μg·m~(-3);晴天(8月22～23日)细粒子昼夜变化明显,夜间在80 m高度出现明显分层,23日80 m以下平均值为32.6±13.1μg·m~(-3),240 m平均值为27.4±13.5μg·m~(-3).雾天细粒子主要来源于局地,霾天细粒子污染表现为时空分布十分均匀的城市群区域污染特征且污染物积累;连续晴天细粒子明显被清除.  相似文献   

19.
Qualification of the sources of volatile organic compounds (VOCs) and their effects on city air pollution are crucial issues to develop an effective air pollution control strategy in many polluted large cities of China. In this study, the VOC concentrations measured in Shanghai, China from 2006 to 2008 are analyzed. A receptor model (PCA/APCS; Principal Component Analysis/Absolute Principal Component Scores) is applied for identifying the contributions of individual VOC sources to VOC concentrations. Using the PCA/APCS technique, five and four surrogated VOC sources are classified in the center of Shanghai city in summer and in winter. In summer, the five VOC sources include PCs1 (liquefied petroleum gas/natural gas leakage and gasoline evaporation), PCs2 (vehicle related emissions), PCs3 (solvent usages), PCs4 (industrial productions), and PCs5 (biomass/biofuel/coal burning and other natural sources). In winter, the four VOC sources include PCw1 (liquefied petroleum gas/natural gas leakage and gasoline evaporation), PCw2 (solvent usages and industrial productions), PCw3 (vehicle related emissions), and PCw4 (biomass/biofuel/coal burning). The result suggests that during summer, 24, 28, 17, 18, and 13% of the measured VOC concentrations were estimated due to the PCs1, PCs2, PCs3, PCs4, and PCs5 VOC sources, respectively. During winter, 17, 48, 23, and 12% of the measured VOC concentrations were attributed to the PCw1, PCw2, PCw3, and PCw4 VOC sources, respectively. For aromatic concentrations, 35% of the concentrations were resulted from solvent usage (PCs3), following by industrial productions (PCs4) of 27%, and vehicle emissions (PCs2) of 19%. For alkene concentrations, the two largest contributors were due to gasoline industrial and vehicle emissions in both summer and winter. For alkane concentrations, the largest sources were due to gasoline industrial emissions (PCs1) and vehicle emissions (PCs2) in summer. In winter, vehicle emissions (PCw3), solvent usages/industrial productions (PCw2), and gasoline industrial emissions (PCw1) were the major sources. For halo-hydrocarbon concentrations, biomass/biofuel/coal burning and other natural sources were the major sources in both summer and winter.  相似文献   

20.
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   

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