首页 | 本学科首页   官方微博 | 高级检索  
相似文献
 共查询到20条相似文献,搜索用时 31 毫秒
1.
Ozone concentrations at a remote site in the Rocky Mountains of southwestern Alberta averaged 43.4 ppb over a 2 year period and the Canadian air quality objective of an 80 ppb hourly average was exceeded 1.5% of the time. The diurnal variation in O3 concentrations was small, 2.9 ppb, indicative of a remote location, above the nocturnal inversion and not greatly influenced by local emissions. During the period when O3 concentrations were highest, winds were generally from the southwest, suggestive of the long range transport of anthropogenic pollutants from distant sources rather than the generation of O3 from local emissions. In contrast, hourly O3 concentrations at two regional air quality monitoring sites showed an average diurnal variation of 14 ppb. Only two hourly averages exceeded 80 ppb during the 2 years, and the mean O3 concentration was 26 ppb. When these regional sites were within the urban plume from Calgary, the O3 concentrations were depressed to a mean of 18 ppb. Ozone concentrations in downtown Calgary averaged 13 ppb. Under Alberta climatological and meteorological conditions, hourly O3 objectives are most likely to be exceeded in remote areas, rather than in cities or in areas under the direct influence of urban emissions.  相似文献   

2.
A time-dependent finite difference model in three levels combined with a puff model to account for subgrid effects close to single sources was used to calculate hour-to-hour concentration distributions. Measurements from several selected stations were used to account from time variation in background concentrations. For each hour, weight was given to observed values in areas that were not influenced by local sources.Results of concentration calculations based on hourly data on emission and dispersion are validated by measured time series of SO2 and NOx at five stations. A combination of hourly nephelometer readings and 12-h measurements of small particles at three stations are compared with calculated values.Hourly observed and calculated values from two periods (3 January–15 March 1988 and 18 April–24 June 1988) were used for the evaluation of the model for calculating hourly pollution concentrations in each square kilometre. The results showed that prediction of short-term average concentrations (e.g. hourly data) are usually poorly correlated with observations at the same time and location. Slight displacement errors may cause point-to-point correlation to be poor as a result of errors in input data.The pattern of NOx concentration variation with time was reproduced well at all stations. A subgrid model taking into account the influence of nearby roads would probably improved the model for NOx at some stations. For SO2 and small particles, industrial sources have the dominant influence and the correspondence between observed and calculated values were improved by taking into account spatial uncertainty and an hourly variation in background concentrations.  相似文献   

3.
被动采样法观测研究京津冀区域大气中气态污染物   总被引:5,自引:3,他引:2  
吴丹  王跃思  潘月鹏  辛金元  唐贵谦 《环境科学》2010,31(12):2844-2851
为了对京津冀区域的大气污染物进行观测,揭示污染物浓度和组分的时空分布和变化规律,深入了解区域复合型污染,从2007年12月开始使用造价低、操作简捷的被动采样方法对区域10个站点大气中的SO2、NO2、O3和NH3等主要污染物进行了监测,对被动采样方法的区域适用性进行了比较全面的评估并根据监测结果对污染物的浓度水平和区域分布进行了研究.方法适用性评估表明被动采样方法在污染较严重的京津冀区域能进行长时间采样,采样频率设定为每月1次;平行采样结果显示,SO2、NO2、O3和NH3的变异系数分别为6.4%、7.1%、4.2%和3.9%,方法表现出良好的稳定性;每月1次的被动采样浓度结果与主动采样仪器观测结果月平均值相比具有较好的一致性,SO2、NO2和O3这2种方法监测结果的相关系数达到0.91、0.88和0.93,拟合曲线斜率分别为1.25、0.98和0.93,平均相对标准偏差分别为23.3%、14.9%和8.5%,能基本满足大气采样的要求,NH3的短时监测也表明2种方法具有可比性.评估结果说明被动采样方法是一种可靠的大气污染监测方法,可用于区域污染的监测.2008年夏季京津冀区域10个站点SO2、NO2、O3和NH3的被动采样平均浓度分别(12.3±6.3)×10-9、(13.2±7.0)×10-9、(40.5±9.5)×10-9和(24.0±13.7)×10-9.浓度区域分布显示SO2和NO2在城市站点具有较高浓度,而NH3在农业站点的浓度较高,SO2、NO2和NH3的大气浓度水平明显受局地排放影响,浓度分布较直观的反应了站点的局地源排放;而O3除了背景站兴隆,在北京和天津周边的大小城市,平均浓度都在40×10-9左右,表现出区域协同污染特征.  相似文献   

4.
Gaseous peroxides play important roles in atmospheric chemistry. To understand the pathways of the formation and removal of peroxides, atmospheric peroxide concentrations and their controlling factors were measured from 7:00 to 20:00 in September, October, and November 2013 at a heavily trafficked residential site in Beijing, China, with average concentrations of hydrogen peroxide (H2O2) and methyl hydroperoxide (MHP) at 0.55 ppb and 0.063 ppb, respectively. H2O2 concentrations were higher in the afternoon and lower in the morning and evening, while MHP concentrations did not exhibit a regular diurnal pattern. Both H2O2 and MHP concentrations increased at dusk in most cases. Both peroxides displayed monthly variations with higher concentrations in September. These results suggested that photochemical activity was the main controlling factor on variations of H2O2 concentrations during the measurement period. Increasing concentrations of volatile organic compounds emitted by motor vehicles were important contributors to H2O2 and MHP enrichment. High levels of H2O2 and MHP concentrations which occurred during the measurement period probably resulted from the transport of a polluted air mass with high water vapor content passing over the Bohai Bay, China.  相似文献   

5.
A simple, inexpensive passive sampler is described that is capable of reliable measurements of formaldehyde at the parts per billion (ppb) levels relevant to indoor and outdoor air quality. The passive sampler consists of a modified dual filter holder in which the upper stage serves as the diffusion barrier, the lower stage includes a 2,4-dinitrophenylhydrazine (DNPH)-coated filter which collects formaldehyde, and the space between the two stages serve as the diffusion gap. The measured sampling rate, 18.8 ± 1.8 ml min−1, was determined in experiments involving sampling of ppb levels of formaldehyde with the passive sampler and with DNPH-coated C18 cartridges and agrees well with the value of 19.4 ± 2.0 ml min−1 calculated from theory. The measured sampling rate was independent of formaldehyde concentration (16–156 ppb) and sampling duration (1.5–72 h). The precision of the measurements for colocated passive samplers averaged 8.6% in purified and indoor air (office and museums) and 10.2% in photochemically polluted outdoor air. With a 1.2-μm pore size Teflon filter as the diffusion barrier, the detection limit is 32 ppb h, e.g. 4 ppb in an 8-h sample, 1.3 ppb in a 24-h sample, and so on. Perceived advantages and limitations of the sampler are discussed including flexibility, cost effectiveness and possible negative bias at high ambient levels of ozone.  相似文献   

6.
The spatial and temporal variability of the daily 1-h maximum O3 concentrations over non-urban areas of the eastern United States of America was examined for the period 1985–1990 using principal component analysis. Utilization of Kaiser's Varimax orthogonal rotation led to the delineation of six contiguous subregions or “influence regimes” which together accounted for 64.02% of the total variance. Each subregion displayed statistically unique O3 characteristics and corresponded well with the path and frequency of anticyclones. When compared to the entire domain, the mid-Atlantic and south subregions observe higher mean daily 1-h maximum concentrations. Concentrations are near the domain average for the northeast and southwest subregions and are lowest in the Great Lakes and Florida subregions. The percentage of observations exceeding 120 ppb were greates in the mid-Atlantic and southwest subregions, near the domain average in the northeast and south subregions, and lowest in the Great Lakes and Florida subregions.Examination of the time series of the principal component scores associated with the subregions indicated that Great Lakes and mid-Atlantic subregions tend to observe a stronger seasonal cycle, with maximum concentrations occurring during the last week in June and first week in July, respectively. The strength of this seasonality is weakened for the northeast and south subregions and its timing delayed, until the end of July and the first of August, respectively. The southwest subregion experiences a greatly diminished seasonality, with maximum concentrations delayed until the middle of August. The seasonality found in the Florida subregion is unique in both its strength and timing, as the highest concentrations consistently occur during the months of April and May. The time series were then deseasonalized and autocorrelations and spectral density estimates calculated, revealing that persistence is much more prevalent in the Florida (autocorrelation significant to a lag of 4 days), south (3 days) and southwest (3 days) subregions. Conversely, autocorrelations are only significant to a lag of one day in the northeast and two days for the Great Lakes and mid-Atlantic subregions.  相似文献   

7.
SO2 measurements made in recent years at sites in Beijing and its surrounding areas are performed to study the variations and trends of surface SO2 at different types of sites in Northern China. The overall average concentrations of SO2 are (16.8 ± 13.1) ppb, (14.8 ± 9.4) ppb, and (7.5 ± 4.0) ppb at China Meteorological Administration (CMA, Beijing urban area), Gucheng (GCH, relatively polluted rural area, 110 km to the southwest of Beijing urban area), and Shangdianzi (SDZ, clean background area, 100 km to the northeast of Beijing urban area), respectively. The SO2 levels in winter (heating season) are 4-6 folds higher than those in summer. There are highly significant correlations among the daily means of SO2 at different sites, indicating regional characteristics of SO2 pollution. Diurnal patterns of surface SO2 at all sites have a common feature with a daytime peak, which is probably caused by the downward mixing and/or the advection transport of SO2-richer air over the North China Plain. The concentrations of SO2 at CMA and GCH show highly significant downward trends (-4.4 ppb/yr for CMA and -2.4 ppb/yr for GCH), while a less significant trend (-0.3 ppb/yr) is identified in the data from SDZ, reflecting the character of SDZ as a regional atmospheric background site in North China. The SO2 concentrations of all three sites show a significant decrease from period before to after the control measures for the 2008 Olympic Games, suggesting that the SO2 pollution control has long-term effectiveness and benefits. In the post-Olympics period, the mean concentrations of SO2 at CMA, GCH, and SDZ are (14.3 ± 11.0) ppb, (12.1 ± 7.7) ppb, and (7.5 ± 4.0) ppb, respectively, with reductions of 26%, 36%, and 13%, respectively, compared to the levels before. Detailed analysis shows that the differences of temperature, relative humidity, wind speed, and wind direction were not the dominant factors for the significant differences of SO2 between the pre-Olympics and post-Olympics periods. By extracting the data being more representative of local or regional characteristics, a reduction of up to 40% for SO2 in polluted areas and a reduction of 20% for regional SO2 are obtained for the effect of control measures implemented for the Olympic Games.  相似文献   

8.
During three large-scale airborne scientific missions (STRATOZ III: June 1984; STRATOZ III-S: March 1985; TROPOZ I: December 1987), the distributions of ozone and its precursors were measured in the tropical belt over the American and African continents, within an altitude range of 0–12 km. The results reveal an important difference between the northern part of South America, characterized in June by an important O3 depletion, and West Africa, where high O3 contents are observed as a result of enhanced formation from bush fires during a large period of the year. O3 concentrations as high as 160 ppb were observed in the neighborhood of emission areas, corresponding to formation rates on the order of several tens of ppb per hour.  相似文献   

9.
This study reports the diurnal patterns in the concentrations of ozone (O3), nitrogen dioxide (NO2), sulphur dioxide (SO2) and total suspended particulate matter (TSP) in the urban atmosphere of Varanasi city in India during 1989. The city was divided into five zones and three monitoring stations were selected in each zone.Ambient concentrations of NO2 and SO2 were maximum during winter but ozone and TSP concentrations were highest during summer. The measured maximum concentrations (2-h average) were 150 and 231 μg m−3 (0.078 and 0.086 ppm) for NO2 and SO2, respectively, for the winter season. Ozone and TSP concentrations reached a maximum of 160 (0.08 ppm) and 733 μg m−3, respectively, in the summer. NO2 and SO2 concentrations peaked in the morning and evening. Peak concentrations of O3 occurred in the afternoon, generally between noon and 4 p.m. Maximum concentrations of O3, NO2, SO2 and TSP were measured in zones I and II, and minimum in zone V.  相似文献   

10.
Indoor and outdoor concentrations of the air pollutants ozone, NO2, SO2, H2S, total reduced sulfur (TRS), peroxyacetyl nitrate (PAN), methyl chloroform and tetrachloroethylene, have been measured at three southern California museums. Indoor maxima were 175 ppb for NO2, 77 ppb for O3, 0.7 ppb for PAN, 1.2 ppb for C2Cl4, >6.3 ppb for CH3CCl3, 2.5 ppb for SO2, 1.4 ppb for TRS, and 46 ppt for H2S. Indoor levels and indoor/outdoor (I/O) ratios for the chlorinated hydrocarbons pointed out to indoor sources. Outdoor and indoor levels of SO2 and TRS were low at all three museums, but I/O ratios for SO2 were high and averaged 0.89. H2S concentrations were low, 16–46 ppt at one museum and less than 6 ppt at the other two museums. I/O ratios for the air pollutants with outdoor sources (ozone, PAN and NO2) showed substantial variations, from low values of 0.02–0.33 at locations without influx of outdoor air to high values of 0.85–0.88 at locations experiencing high influx of outdoor air. Of the 10 institutions we have surveyed in southern California to date, eight exhibit high I/O ratios, e.g. 0.60–1.00 for PAN. Of the four museums surveyed that were equipped with HVAC and chemical filtration, only two yielded the expected low I/O ratios.  相似文献   

11.
Ground-level ozone and oxidant (sum of O3 and NO2) concentrations in The Netherlands are calculated during the growing season (May–September) by means of a Lagrangian long-range transport model. Two air parcels—one representative of the mixed layer, the other representative of the polluted layer above the mixed layer (aged smog layer)—are followed along 96 h back trajectories. Long-term averaged and 98 percentile values of hourly averaged concentrations are estimated on the basis of concentrations calculated for four arrival times per day for all days in the period considered.In a number of sensitivity runs the influence of European anthropogenic NOx and VOC emissions on the oxidant concentrations in The Netherlands has been investigated. In general, the influence of European emissions on the 98-percentile values is 2–3 times as large as on the averaged concentrations. This indicates that long-term averaged concentrations more strongly depend on the concentrations in the free troposphere whereas the episodic concentrations are determined by photochemical production over Europe. VOC emission reduction is more effective in lowering episodic concentrations than NOx emission reduction. For long-term averaged concentrations, however, NOx and VOC emission reduction of 50% or more are nearly equally effective.  相似文献   

12.
采用在线仪器监测分析2017年夏季天津气象铁塔220 m观测平台大气中过氧乙酰硝酸酯(PAN)和O_3的体积分数,并结合气象观测资料和后向轨迹分析PAN和O_3的输送特征.观测期间PAN和O_3体积分数平均值分别为(0.73±0.56)×10~(-9)和(53±25)×10~(-9),最大小时体积分数分别为3.49×10~(-9)和137×10~(-9),PAN和O_3体积分数具有相似的日变化特征,白昼PAN和O_3浓度高于夜间,且PAN和O_3浓度相关系数(R2=0.52)显著高于夜间(R2=0.21).观测期间偏南风下PAN和O_3浓度最高,偏东风下最低,风玫瑰图和后向轨迹聚类分析都表明,来源于西南方向的气流轨迹对应的污染物浓度最高,途经渤海和河北、辽宁沿海地区的偏东气流对应的PAN和O_3体积分数最低,边界层内输送对PAN和O_3的体积分数分布起到了重要作用.  相似文献   

13.
During the 15 January–4 February 1986 SCENES Special Study, a comparison study was conducted to determine atmospheric HNO3 (g), HNO2 (g), SO2 (g), and particle-phase nitrate, nitrite and sulfate sampled with annular diffusion denuder and filter pack sampling systems for 12-h periods. The results of the ion chromatographic analyses of the denuder and filter extracts from the annular denuder system showed that an average of 88% of the total nitrate measured was HNO3 (g), 97% of the total nitrite was HNO2 (g), and 91% of the total sulfur was present as SO2 (g). Analyses of the various gas-phase species collected by replicate annular denuder systems indicated that a precision of ± 3% to ± 18% was achieved using these denuders. The good agreement in HNO3 (g) concentrations observed between the filter pack and the denuder (r2=0.873, slope=1.06±0.03, intercept=0±3.5 nmol m−3) results from the fact that the majority of the atmospheric nitrate consisted of HNO3 (g), which minimized any positive artifact in HNO3(g) due to loss of HNO3(g) from particles collected in the filter pack. The particulate-phase nitrate correlation between the two sampling systems was not as good (r2=0.709, slope=0.519±0.045, intercept =0±1.2 nmol m−3) because the lower percentage of nitrate present as the particulate species was more affected by the loss of particulate nitrate during sampling with the filter pack.  相似文献   

14.
Most previous O3 simulations were based only on gaseous phase photochemistry. However, some aerosol-related processes, namely, heterogeneous reactions occurring on the aerosol surface and photolysis rate alternated by aerosol radiative influence, may affect O3 photochemistry under high aerosol loads. A three-dimensional air quality model, Models-3/Community Multi-scale Air Quality-Model of Aerosol Dynamics, Reaction, Ionization, and Dissolution, was employed to simulate the effects of the above-mentioned processes on O3 formation under typical high O3 episodes in Beijing during summer. Five heterogeneous reactions, i.e., NO2, NO3, N2O5, HO2, and O3, were individually investigated to elucidate their effects on O3 formation. The results showed that the heterogeneous reactions significantly affected O3 formation in the urban plume. NO2 heterogeneous reaction increased O3 to 90 ppb, while HO2 heterogeneous reaction decreased O3 to 33 ppb. In addition, O3 heterogeneous loss decreased O3 to 31 ppb. The effects of NO2, NO3, and N2O5 heterogeneous reactions showed opposite O3 concentration changes between the urban and extra-urban areas because of the response of the reactions to the two types of O3 formation regimes. When the aerosol radiative influence was included, the photolysis rate decreased and O3 decreased significantly to 73 ppb O3. The two aerosol-related processes should be considered in the study of O3 formation because high aerosol concentration is a ubiquitous phenomenon that affects the urban- and regional air quality in China.  相似文献   

15.
采用南京工业区2016年5月20日~8月15日这一高臭氧(O3)期的O3、O3前体物和常规气象资料数据,利用支持向量机回归(SVMr)方法分别预报O3的小时值、日最大值和最大8 h滑动平均值.结果表明,O3小时值预报的相关系数(R2)为0.84,平均绝对误差(MAE)和平均绝对百分误差(MAPE)分别为3.44×10-9和24.48,O3前期浓度、紫外B波段辐射(UVB)和NO2浓度是关键因子.O3日最大值预报的主要因子是NOx在07:00的浓度和UVB.预报O3 8 h时UVB和气温起重要作用.加入前体物项能够使O3的预报精度提升10%~28%.与多元线性回归方法相比,SVMr对O3浓度的预报有明显优势.  相似文献   

16.
Mass level of fine particles (PM2.5) in main cities in China has decreased significantly in recent years due to implementation of Chinese Clean Air Action Plan since 2013, however, O3 pollution is getting worse than before, especially in megacities such as in Shanghai. In this work, O3 and PM2.5 were continuously monitored from May 27, 2018 to March 31, 2019. Our data showed that the annual average concentration of PM2.5 and O3 (O3-8 hr, maximum 8-hour moving average of ozone days) was 39.35 ± 35.74 and 86.49 ± 41.65 µg/m3, respectively. The concentrations of PM2.5 showed clear seasonal trends, with higher concentrations in winter (83.36 ± 18.66 µg/m3) and lower concentrations in summer (19.85 ± 7.23 µg/m3), however, the seasonal trends of O3 were different with 103.75 ± 41.77 µg/m3 in summer and 58.59 ± 21.40 µg/m3 in winter. Air mass backward trajectory, analyzing results of potential source contribution function model and concentration weighted trajectory model implied that pollutants from northwestern China contributed significantly to the mass concentration of Shanghai PM2.5, while pollutants from areas of eastern coastal provinces and South China Sea contributed significantly to the mass level of ozone in Shanghai atmosphere. Mass concentration of twenty-one elements in the PM2.5 were investigated, and their relationships with O3 were analyzed. Mass level of ozone had good correlation with that of Ba (r = 0.64, p < 0.05) and V (r = 0.30, p > 0.05), suggesting vehicle emission pollutants contribute to the increasing concentration of ozone in Shanghai atmosphere.  相似文献   

17.
Measurements of HONO and HNO3 have been made using annular denuder samplers at sites in south-east England. Whilst concentrations of HNO3 exhibited a diurnal variation, with a maximum in mid-afternoon nitrous acid shows the opposite diurnal cycle with maximum levels at night due to daytime photolysis. Concentrations of HONO increase with those of NO2, and elevated nighttime HONO level appear to be followed by high levels of HNO3 the following day. Average concentrations of HONO (0.45± 0.26 ppb in 24 h samples are comparable to those of HNO3 (0.56±0.36 ppb in 24 h samples), each representing about 5–10% of the concentration of NO2. Although NO2 oxidation provides the source of HNO3 concentrations of the two compounds are not related, presumably since the formation of NH4NO3 aerosol limits HNO3 concentrations at out site.  相似文献   

18.
The nitrate radical (NO3) and dinitrogen pentoxide (N2O5) play an important role in the nocturnal atmosphere chemistry. Observations of NO3 radicals and N2O5 were performed in a semirural ground site at Tai'Zhou in polluted southern China using cavity ring down spectroscopy (CRDS) from 23 May to 15 June 2018. The observed NO3 and N2O5 concentrations were relatively low, with 1 min average value of 4.4 ± 2.2 and 26.0 ± 35.7 pptV, respectively. The N2O5 uptake coefficient was determined to be from 0.027 to 0.107 based on steady state lifetime method. Fast N2O5 hydrolysis was the largest contributor to the loss of NO3 and contributed to substantial nitrate formation, with an average value of 14.83 ± 6.01 µg/m3. Further analysis shows that the N2O5 heterogeneous reactions dominated the nocturnal NOx loss and the nocturnal NOx loss rate is 0.14 ± 0.02 over this region.  相似文献   

19.
Gas chromatography with ambient temperature injection and frozen-trapped techniques was used to determine the atmospheric concentrations of halocarbons over Beijing. Halogenated compounds such as CFC-11, CFC-12, CHCl_3, CCl_4, CH_3CCl_3, CHCl =CCl_2, and CCl_2=CCl_2 were measured and their concentrations are 109±8, 234±13, 47±22, 97±24, 88±29, 11±1 and 17±3 (pptv), respectively.  相似文献   

20.
Using data obtained during the 1985 Nitrogen Species Methods Comparison Study (1988,Atmospheric Environment22, 1517), several measurement methods for sampling ambient NH3 are compared. Eight days of continuous measurements at Pomona College, a smog receptor site in Los Angeles, provided an extensive data base for comparing the following methods: Fourier transform i.r. spectroscopy (FTIR), three filter pack configurations, a simple and an annular denuder, and the transition flow reactor. FTIR was defined as the reference method and it reported hourly NH3 concentrations ranging from > 60 to 2280 nmol m−3 (1.5−57ppb) during the course of the study, the highest values coming from the influence of nearby livestock operations.Although only limited quality assurance procedures were carried out, the following conclusions can, nevertheless, be drawn: most of the methods correlated highly with the FTIR method (correlation coefficientr > 0.96); generally, the linear regression slopes were close to unity and the intercepts were insignificantly different from zero at the 95% confidence level); relative to the FTIR average values, (1) for 4–6 h sampling periods, the averages of the three filter packs from three research groups were 83–130% and the annular denuder average was 87%, and (2) for 10–12 h sampling periods, the simple denuder averaged 90% and the two transition flow reactors were 77–98%. Possible reasons for the reported systematic biases are presented, but these are not able to fully explain the large range of differences reported by the various methods.  相似文献   

设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号