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1.
Summary  In the central region of Taiwan, ozone episodes occur most often during autumn. Two field experiments were conducted during the autumns of 1998 and 1999 to analyze the vertical profile of the boundary layer and determine its effects on ozone concentration over the region. The vertical virtual potential temperature and wind profiles were derived from tethersonde data. The NOx, NMHC and O3 concentration vertical profiles were monitored up to a height of 500 meters using black-covered Teflon tedler sampling bags. During the experimental periods, nighttime terrestrial long wave radiation could cause the inversion height to reach 500 meters by the following morning. It was shown that these types of synoptic structures suppress the vertical diffusion of NOx, NMHC and O3. During the daytime, measurements indicate that pollutants were well mixed in the upper portion of the mixing layer. At night, the ground level ozone concentration was on the decrease but increased with altitude to a height of 500 m. The NOx decreased with altitude whereas the NMHC showed no significant variations. Received April 13, 2000 Revised July 24, 2000  相似文献   

2.
Climate change has been receiving wide attention in the last few decades. In order to quantify the climate variability of extreme weather events and their possible impacts on weather parameters and air quality, cold surge events in the past 45 years and the difference in characteristics of air pollutants before and after frontal passage has been examined after December 1993 in Taiwan. The potential impact of climate change on air pollutant concentration and its health implication were presented and discussed. In the past 45 years, the cold surge days (about 18.7 days, or 0.42 day/year) decreased significantly and the average lowest daily temperature for winter in northern Taiwan increased nearly 3°C (0.067°C/year). Based on the definition of cold surge in Taiwan and excluding the stagnation frontal passage, 21 cold surge frontal passage (CSFP) cases and 89 common frontal passage (CFP) events in winter (December–February) were identified in the past 12 years (1993–2005). We take the frontal passage day as the baseline and the differences in air pollutant concentrations and weather-related parameters between the two days before and after the frontal passage days were examined for each case. The averages of the above-mentioned differences during CSFP were compared to the corresponding differences during CFP. During CSFP, the air temperatures after the frontal passage were nearly 4–6°C lower than before the passage at both the background windward stations and urban stations. The average wind speed was about 4–5 m/s higher at the windward stations and less than 2 m/s higher in the major urban areas in Taiwan. During CFP, there was a 2°C increase in temperature but 1 m/s decrease in wind speeds on the day after frontal passage. Because of these meteorological differences, the concentration change of air pollutants during CSFP is significantly greater than that during CFP, especially for PM10 concentration. The difference of PM10 concentration during CSFP can be as large as 20–40 μg/m3 while that during CFP is only about 10 μg/m3. The differences in the other air pollutants such as CO, SO2, and O3 during CSFP are greater than those during CFP, but the difference is insignificant. Under the warming trend, less frequent CSFP’s are expected; the impacts on deterioration of air quality and human health are noteworthy.  相似文献   

3.
近年来近地面臭氧问题日益凸显,成为影响空气质量持续改善的瓶颈.本研究基于2017年8—9月在湖州市城区开展的为期1个月的臭氧及其前体物挥发性有机物（VOCs）和氮氧化物（NOx）在线观测数据,分析了臭氧及其前体物污染特征,利用正矩阵因子分析（PMF）解析了VOCs来源,并采用基于观测的模型（OBM）对臭氧生成机制进行研究.研究结果表明：1）观测期间湖州市VOCs平均体积分数为（24.78±9.10）×10-9,其中占比最高的组成为烷烃、含氧VOCs （OVOCs）和卤代烃;2）在臭氧非超标时段,湖州市臭氧生成处于VOCs控制区,而在臭氧重污染期间湖州市处于以VOCs控制为主的过渡区;3）在臭氧超标时段,对臭氧生成潜势（OFP）贡献最大的是芳香烃（39.6%）,其次是烯烃（21.5%）和OVOCs （19.4%）,排名前三的关键组分为甲苯、乙烯和间/对二甲苯;4）源解析结果显示观测期间湖州市VOCs的主要来源是溶剂使用（27.0%）、交通排放（22.7%）、背景+传输（19.3%）、工业排放（16.9%）、汽油挥发（7.7%）和植物排放（6.4%）,重污染过程期间对OFP贡献最大的两类源是交通排放源和溶剂使用源,贡献百分比分别为35.1%和30.5%.因此,对交通排放和溶剂使用方面进行控制管理对湖州市大气臭氧污染防控有重要意义.  相似文献   

4.
Summary The three-dimensional long-range transport model EURAD has been applied to two episodes in 1986 to study the transport and transformation of air pollutants over Europe under different meteorological conditions. The spring episode is characterized by varying meteorological conditions over Europe and transport of pollutants is complex. The summer episode is suitable to study the enhanced formation of photooxidants as an almost stagnant high pressure system over central Europe favoured the accumulation of pollutants. Available observations from several monitoring networks in Europe are used to evaluate the near surface concentration predictions of the model. This is possible for the sulfur species, O3 and NO2 for the central part of the modelling domain. It is shown that O3 and NO2 trends in the western part of the model domain are estimated reasonably well. The strong bias for underpredicting NO2 in the eastern part of the domain reflects the quality of emission data for the two regions of the modelling area. Typically for regional scale Eulerian transport models when applied on larger grid sizes, EURAD overpredicts the observed minima and underpredicts the high observations. This is particularly true for O3 but also detectable in the sulfate comparisons. Several sensitivity simulations for both episodes were performed to test numerical algorithms, parameterizations or emission data. Results from these simulations clearly show the important role of cloud related processes during the spring time for the sulfur species. Further testing and assessment of cloud parameterizations and emission data for transport models is anticipated.With 22 Figures  相似文献   

5.
In order to study the concentrations of hydrogen peroxide (H2O2) and the factors controlling its concentrations, we monitored concentrations of H2O2 and other gases such as sulfur dioxide, ozone, and NO x as well as meteorological factors such as air temperature, relative humidity, and wind direction/speed during eight measurement periods from 2000 to 2002 in a Japanese red pine forest in Japan. The H2O2 concentrations ranged from below 0.01 to 1.64 ppb, and analysis of the diurnal variation in H2O2 concentration showed high concentrations around noon, and low concentrations in the morning and late afternoon. The H2O2 concentrations were high in early summer, when O3 concentration, temperature, and solar radiation were high, and were low in fall, when O3 concentration, temperature, and solar radiation were low. We propose that O3 concentration affects the production of H2O2 in the monitored region during the period under study, but that high H2O2 concentrations were sometimes caused by the transport of polluted air from urban regions. H2O2 concentrations decreased remarkably when SO2 concentrations increased by transported volcanic emission on Miyake Island. In the absence of the effects of SO2, H2O2 concentrations increased with increasing O3 concentration and temperature.  相似文献   

6.
近年来武汉市臭氧污染日益严峻,成为影响空气质量达标的瓶颈,弄清臭氧及其前体物非线性关系是臭氧防控的关键和基础.本研究基于武汉中心城区2018年4—9月臭氧及其前体物在线观测数据,分析出武汉市臭氧浓度受前体物和气象条件等因素的共同影响,呈较为明显的季节变化和日变化特征.观测期间武汉市大气挥发性有机物（VOCs）平均体积分数为32.5×10-9,烷烃是武汉市VOCs的主要组分,其次是含氧VOCs （OVOCs）和卤代烃.利用基于观测的模型定量分析臭氧与前体物之间的关系,发现削减VOCs会引起臭氧生成潜势的显著下降,而削减氮氧化物则会使臭氧生成潜势升高,说明武汉市臭氧生成处于VOCs控制区.在人为源VOCs中,间/对二甲苯和邻二甲苯的相对增量反应活性（RIR）最高,是影响臭氧生成的关键组分.  相似文献   

7.
Summary Air pollution measurements from January 1999 to December 2003 were studied in 14 sites covering most of Egypt, with the aim of understanding the governing processes pollutants phase interaction. The nature of the contributing sources has been investigated, and some attempts have been made to indicate the role played by neighboring regions in determining the air quality at these sites. The seasonal variability of particulate matter (PM10) and some gaseous pollutants (e.g., SO2, NO2, CO and O3) were analyzed. Their relationships with meteorology were also examined. The results reveal that levels of major air pollutants were not significantly different at the rural and background sites during any season. On contrary the high atmospheric loading for PM10, CO and SO2 was frequently observed in winter at the urban sites. As expected, the prevailing winds were found to have an influence not only on air pollutants but also on the correlation between them.  相似文献   

8.
The CHIMERE mesoscale chemistry transport model is used for the quantitative assessment of the contribution of transboundary transport of anthropogenic admixtures from China to the surface concentrations of major suspended pollutants, aerosol PM10, ozone O3, and nitrogen oxides NOx in the Far Eastern region. Analyzed in detail are the time series of concentration of mentioned substances computed with the model taking account and not taking account of anthropogenic emissions in China. It is revealed that the transboundary transport of anthropogenic pollutants can cause the recurring episodes of manyfold increase in the concentration of PM10 in the south of Khabarovsk region, as well as more rare variations of O3 and NOx concentration. The trajectory and synoptic analysis demonstrated that the episodes of the increase in the concentration of PM10 and O3 in the south of the region mainly depend on the carryover of air masses from northeastern China in the front part of continental cyclones.  相似文献   

9.
Continuous measurements of surface ozone (O3), NOx (NO + NO2) and meteorological parameters have been made in Kannur (11.9?°N, 75.4?°E, 5?m asl), India from November 2009 to October 2010. It was observed that O3 and NOx showed distinct diurnal and seasonal variabilities at this site. The annual average diurnal profile of O3 showed a peak of (30.3?±?10.4) ppbv in the late afternoon and a minimum of (3.2?±?0.7) ppbv in the early morning. The maximum value of O3 mixing ratio was observed in winter (44?±?3.1) ppbv and minimum during monsoon (18.46?±?3.5) ppbv. The rate of production of O3 was found to be higher in December (10.1?ppbv/h) and lower in July (1.8?ppbv/h) during the time interval 0800?C1000?h. A correlation coefficient of 0.52 for the relationship between O3 and [NO2]/[NO] reveals the role of NO2 photolysis that generates O3 at this site. The correlation between O3 and meteorological parameters indicate the influence of seasonal changes on O3 production. Investigations were further extended to explore the week day weekend variations in O3 mixing ratio at an urban site reveals the enhancement of O3. The variations of O3 mixing ratio with seasonal air mass flows were elucidated with the aid of backward air trajectories. This study also indicates how vapor phase organic species present in the ambient air at this location may influence the complex chemistry involving (VOCs) that enhances the production of O3 at this location.  相似文献   

10.
Tropospheric distributions of ozone (O3) and water vapor (H2O) have been presented based on the Measurements of OZone and water vapor by Airbus In-Service AirCraft (MOZAIC) data over the metro and capital city of Delhi, India during 1996–2001. The vertical mixing ratios of both O3 and H2O show strong seasonal variations. The mixing ratios of O3 were often below 40 ppbv near the surface and higher values were observed in the free troposphere during the seasons of winter and spring. In the free troposphere, the high mixing ratio of O3 during the seasons of winter and spring are mainly due to the long-range transport of O3 and its precursors associated with the westerly-northwesterly circulation. In the lower and middle troposphere, the low mixing ratios of ∼20–30 ppbv observed during the months of July–September are mainly due to prevailing summer monsoon circulation over Indian subcontinent. The summer monsoon circulation, southwest (SW) wind flow, transports the O3-poor marine air from the Arabian Sea and Indian Ocean. The monthly averages of rainfall and mixing ratio of H2O show opposite seasonal cycles to that of O3 mixing ratio in the lower and middle troposphere. The change in the transport pattern also causes substantial seasonal variation in the mixing ratio of H2O of 3–27 g/kg in the lower troposphere over Delhi. Except for some small-scale anomalies, the similar annual patterns in the mixing ratios of O3 and H2O are repeated during the different years of 1996–2001. The case studies based on the profiles of O3, relative humidity (RH) and temperature show distinct features of vertical distribution over Delhi. The impacts of long range transport of air mass from Africa, the Middle East, Indian Ocean and intrusions of stratospheric O3 have also been demonstrated using the back trajectory model and remote sensing data for biomass burning and forest fire activities.  相似文献   

11.
This study examines the processes controlling the diurnal variability of ozone (O3) in the marine boundary layer of the Kwajalein Atoll, Republic of the Marshall Islands (latitude 8° 43′ N, longitude 167° 44′ E), during July to September 1999. At the study site, situated in the equatorial Pacific Ocean, O3 mixing ratios remained low, with an overall average of 9–10 parts per billion on a volume basis (ppbv) and a standard deviation of 2.5 ppbv. In the absence of convective storms, daily O3 mixing ratios decreased after sunrise and reached minimum during the afternoon in response to photochemical reactions. The peak-to-peak amplitude of O3 diurnal variation was approximately 1–3 ppbv. During the daytime, O3 photolysis, hydroperoxyl radicals, hydroxyl radicals, and bromine atoms contributed to the destruction of O3, which explained the observed minimum O3 levels observed in the afternoon. The entrainment of O3-richer air from the free troposphere to the local marine boundary layer provided a recovery mechanism of surface O3 mixing ratio with a transport rate of 0.04 to 0.2 ppbv per hour during nighttime. In the presence of convection, downward transport of O3-richer tropospheric air increased surface O3 mixing ratios by 3–12 ppbv. The magnitude of O3 increase due to moist convection was lower than that observed over the continent (as high as 20–30 ppbv). Differences were ascribed to the higher O3 levels in the continental troposphere and weaker convection over the ocean. Present results suggest that moist convection plays a role in surface-level O3 dynamics in the tropical marine boundary layer.  相似文献   

12.
During the summer (8 June through 3 September) of 2008, 9 ozone profiles are examined from Dakar, Senegal (14.75°N, 17.49°W) to investigate ozone (O3) variability in the lower/middle troposphere during the pre-monsoon and monsoon periods. Results during June 2008 (pre-monsoon period) show a reduction in O3 concentrations, especially in the 850–700 hPa layer with Saharan Air Layer (SAL) events. However, O3 concentrations are increased in the 950–900 hPa layer where the peak of the inversion is found and presumably the highest dust concentrations. We also use the WRF-CHEM model to gain greater insights for observations of reduced O3 concentrations during the monsoon periods. In the transition period between 26 June and 2 July in the lower troposphere (925–600 hPa), a significant increase in O3 concentrations (10–20 ppb) occur which we suggest is caused by enhanced biogenic NOX emissions from Sahelian soils following rain events on 28 June and 1 July. The results suggest that during the pre-monsoon period ozone concentrations in the lower troposphere are controlled by the SAL, reducing ozone concentrations through heterogeneous chemical processes. At the base of the SAL we also find elevated levels of ozone, which we attribute to biogenic sources of NOX from Saharan dust that are released in the presence of moist conditions. Once the monsoon period commences, lower ozone concentrations are observed and modeled which we attribute to the dry deposition of ozone and episodes of ozone poor air that is horizontally transported into the Sahel from low latitudes by African Easterly Waves (AEWs).  相似文献   

13.
Continuous in-situ measurements of surface ozone (O3), carbon monoxide (CO) and oxides of nitrogen (NOx) were conducted at Udaipur city in India during April 2010 to March 2011. We have analyzed the data to investigate both diurnal and seasonal variations in the mixing ratios of trace gases. The diurnal distribution of O3 showed highest values in the afternoon hours and lower values from evening till early morning. The mixing ratios of CO and NOx showed a sharp peak in the morning hours but lowest in the afternoon hours. The daily mean data of O3, CO and NOx varied in the ranges of 5–51 ppbv, 145–795 ppbv and 3–25 ppbv, respectively. The mixing ratios of O3 were highest of 28 ppbv and lowest 19 ppbv during the pre-monsoon and monsoon seasons, respectively. While the mixing ratios of both CO and NOx showed highest and lowest values during the winter and monsoon seasons, respectively. The diurnal pattern of O3 is mainly controlled by the variations in photochemistry and planetary boundary layer (PBL) depth. On the other hand, the seasonality of O3, CO and NOx were governed by the long-range transport associated mainly with the summer and winter monsoon circulations over the Indian subcontinent. The back trajectory data indicate that the seasonal variations in trace gases were caused mainly by the shift in long-range transport pattern. In monsoon season, flow of marine air and negligible presence of biomass burning in India resulted in lowest O3, CO and NOx values. The mixing ratios of CO and NOx show tight correlations during winter and pre-monsoon seasons, while poor correlation in the monsoon season. The emission ratio of ?CO/?NOx showed large seasonal variability but values were lower than those measured over the Indo Gangetic Plains (IGP). The mixing ratios of CO and NOx decreased with the increase in wind speed, while O3 tended to increase with the wind speed. Effects of other meteorological parameters in the distributions of trace gases were also noticed.  相似文献   

14.
中美大气化学联合考察实验结果的初步分析与比较   总被引：1，自引：0，他引：1  
根据临安区域本底站观测资料分析结果得出,中国中纬度地区秋、冬季O3及其前体物NOx等浓度偏高,可以对农作物和地表生态系统产生影响.观测结果表明:近地层大气O3浓度主要决定于地面总辐射量控制下的光化学反应过程;O3的生成受到前体物NOx的控制,但O3与NOx存在着明显的非线性关系.从PEM-WESTA和B的实验及1995年的观测资料表明,O3的生成效率随着NOx浓度的增大而减小.尽管O3的生成速率秋季比冬季的大,但由于秋季较高的NOx抑制了过氧基的生成,因此冬季O3的累积量几乎可以和秋季相比拟.在临安观测的NMHC和NOx的比值比国外同纬度地区测值要大.这说明在临安本底站O3的光化学生成中,NMHC不是控制物种.从而提示我们,在这些季节临安O3光化学产物能够被NOx浓度所控制.中美大气化学联合考察(PEM-WEST-B)实验期间,台湾省的卡盯站SO2的平均浓度为0.29ppb,O3的平均浓度为42.2ppb,可以认为此值为低纬度海岛的本底值.1994年PEM-WEST-B实验期间临安站的观测资料和台湾省的卡盯站资料相比,临安站SO2的浓度约为卡盯站SO2浓度的50倍左右,从而可以看出人类活动对大气本底的显着影响.  相似文献   

15.
Continuous measurements of ozone and its precursors including NO, NO2, and CO at an urban site (32°03′N, 118°44′E) in Nanjing, China during the period from January 2000 to February 2003 are presented. The effects of local meteorological conditions and distant transports associated with seasonal changed Asian monsoons on the temporal variations of O3 and its precursors are studied by statistical, backward trajectory, and episode analyses. The diurnal variation in O3 shows high concentrations during daytime and low concentrations during late night and early morning, while the precursors show high concentrations during night and early morning and low concentrations during daytime. The diurnal variations in air pollutants are closely related to those in local meteorological conditions. Both temperature and wind speed have significant positive correlations with O3 and significant negative correlations with the precursors. Relative humidity has a significant negative correlation with O3 and significant positive correlations with the precursors. The seasonal variation in O3 shows low concentrations in late autumn and winter and high concentrations in late spring and early summer, while the precursors show high concentrations in late autumn and winter and low concentrations in summer. Local mobile and stationary sources make a great contribution to the precursors, but distant transports also play a very important role in the seasonal variations of the air pollutants. The distant transport associated with the southeastern maritime monsoon contributes substantially to the O3 because the originally clean maritime air mass is polluted when passing over the highly industrialized and urbanized areas in the Yangtze River Delta. The high frequency of this type of air mass in summer causes the fact that a common seasonal characteristic of surface O3 in East Asia, summer minimum, is not observed at this site. The distant transports associated with the northern continental monsoons that dominate in autumn and winter are related to the high concentrations of the precursors in these two seasons. This study can contribute to a better understanding of the O3 pollution in vast inland of China affected by meteorological conditions and the rapid urbanization and industrialization.  相似文献   

16.
Measurements of surface O3, CO, NOx and light NMHCs were made during December 2004 at Hissar, a semi-urban site in the state of Haryana in north-west region of the Indo-Gangetic Plain (IGP). The night-time O3 values were higher when levels of CO, NO and NO2 were lower but almost zero values were observed during the episodes of elevated mixing ratios of CO (above 2000 ppbv) and NOx (above 50 ppbv). Slopes derived from linear fits of O3 versus CO and O3 versus NOx scatter plots were also negative. However, elevated levels of O3 were observed when CO and NOx were in the range of 200–300 ppbv and 20–30 ppbv, respectively. Slope of CO-NOx of about 33 ppbv/ppbv is much larger than that observed in the US and Europe indicating significant impact of incomplete combustion processes emitting higher CO and lesser NOx. Correlations and ratios of these trace gases including NMHCs show dominance of recently emitted pollutants mostly from biomass burning at this site.  相似文献   

17.
Surface ozone (O3) and fine particulate matter (PM2.5) are dominant air pollutants in China. Concentrations of these pollutants can show significant differences between urban and nonurban areas. However, such contrast has never been explored on the country level. This study investigates the spatiotemporal characteristics of urban-to-suburban and urban-to-background difference for O3 (Δ[O3]) and PM2.5 (Δ[PM2.5]) concentrations in China using monitoring data from 1171 urban, 110 suburban, and 15 background sites built by the China National Environmental Monitoring Center (CNEMC). On the annual mean basis, the urban-to-suburban Δ[O3] is ?3.7 ppbv in Beijing–Tianjin–Hebei, 1.0 ppbv in the Yangtze River Delta, ?3.5 ppbv in the Pearl River Delta, and ?3.8 ppbv in the Sichuan Basin. On the contrary, the urban-to-suburban Δ[PM2.5] is 15.8, ?0.3, 3.5 and 2.4 μg m?3 in those areas, respectively. The urban-to-suburban contrast is more significant in winter for both Δ[O3] and Δ[PM2.5]. In eastern China, urban-to-background differences are also moderate during summer, with ?5.1 to 6.8 ppbv for Δ[O3] and ?0.1 to 22.5 μg m?3 for Δ[PM2.5]. However, such contrasts are much larger in winter, with ?22.2 to 5.5 ppbv for Δ[O3] and 3.1 to 82.3 μg m?3 for Δ[PM2.5]. Since the urban region accounts for only 2% of the whole country’s area, the urban-dominant air quality data from the CNEMC network may overestimate winter [PM2.5] but underestimate winter [O3] over the vast domain of China. The study suggests that the CNEMC monitoring data should be used with caution for evaluating chemical models and assessing ecosystem health, which require more data outside urban areas.  相似文献   

18.
At Amphitrite Point, ozone (O3) mixing ratios are observed to drop steadily to 5–15?ppb over a period of 12 hours or less with a frequency approaching one event per week (with highest frequencies occurring in summer and fall). Analysis of 47 such O3 depletion events reveals that low O3 episodes are a predominantly nocturnal phenomenon associated with anticyclonic conditions characterized by light onshore or alongshore winds and an absence of fog and mist. Back-trajectories show air carried to the Amphitrite Point Observatory (APO) during depletion events remains in the marine boundary layer and is not brought to the surface from aloft. There is no strong correlation with other “criteria” pollutants (CO, NOx, SO2, PM2.5) that might be indicative of a mechanism for O3 destruction linked to human, terrestrial, or marine pollutant sources. However, CO2 mixing ratios are observed to increase, coincident with O3 depletion. Together, these results point to a natural marine boundary layer phenomenon in which O3 destruction dominates O3 production and/or replenishment by vertical mixing. While there are several candidate mechanisms, the conditions for O3 depletion (and CO2 buildup) to occur are set by meteorology and, in particular, development of a stable marine boundary layer in which vertical mixing is suppressed. Support for this interpretation is provided by simultaneous increases in CO2 in the stable marine boundary that are indicative of an important role played by marine biogenic processes (respiration). Future research should be directed at elucidating the chemical mechanisms responsible for O3 destruction in the coastal zone, which means that there would be a need for a much broader range of measurements at APO (including halogenated species) as well as offshore measurements of both chemical and marine boundary layer meteorological variables.  相似文献   

19.
Atmospheric peroxides and formaldehyde were measured at two sites in Sweden; inside a Scots pine stand (Jädraås) and on top of Mt. Åreskutan (1250 msl). Peroxide levels at Jädraås were highest during the day and lowest during the night. Mid-day concentrations of H2O2 varied between 0.05 and 2 ppbv. Isentropic trajectories together with local O3 measurements indicated the importance of long range transport on surface H2O2 lévels. Large diurnal variations and vertical profiles showed the importance of turbulent mixing processes and dry deposition. A comparison of H2O2 and O3 diurnal variations indicated a more rapid dry deposition of H2O2 to the forest. It would appear that terpenes emitted from the forest play a minor role in controlling the H2O2 levels. Formaldehyde at Jädraås had a different diurnal variation than peroxides; highest levels were observed in the early evening indicating chemical production of CH2O. Diurnal variations of peroxides on Mt Åreskutan were opposite to those at Jädraås, highest concentrations were observed during the night. This result is to be expected if during the day air from inside the valley, with lower peroxide levels relative to the free troposphere, rises to the mountain top. In the evening, subsidence brings free tropospheric air with higher peroxides levels to the mountain.  相似文献   

20.
A high O3 episode was observed during 23–25 May 2004 at two high-mountain sites reflecting the regional pattern of air pollutants over East China. This episode lasted about three days with the maximum hourly O3 mixing ratios reaching 111 and 114 ppbv at Mt. Tai and Huang, respectively. Backward trajectories and meteorological analysis indicated that regional transport, associated with a weak high pressure system over the East China Sea, might play an important role in the formation of this high ozone episode. The nested air quality prediction modeling system (NAQPMS) was applied to investigate the formation and evolution of this high O3 event. The comparison of model results with observations showed that NAQPMS successfully reproduced the main observed patterns of O3 and meteorological parameters during the simulated period. The model results with emission over the Yangtze Delta and the East Central China switched on/off clearly showed that ozone and its precursors transported from the Yangtze Delta and the East Central China enhanced the high ozone episode at two sites, with a contribution of 20%–50% during the episode. In addition, based on process analysis with the model, chemical production and regional transport appeared to be the main causes of high ozone episode involving a large amount of high-ozone air masses and precursors transported from the surrounding areas. The horizontal transport is more active during the period of high ozone episode than that during the non-episode at Mt. Tai as well as Mt. Huang.  相似文献   

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