air pollution control.docx

华东理工大学20152016学年第二学期大气污染控制工程课程论文 2016.4班级 环境133 学号 10132228 姓名 周嘉昊 开课学院 资环学院 任课教师 杨骥 成绩 论文题目：论文要求：The term paper is required for all students registered in this course. This writing assignment MUST be written in English!Purpose: Each student is expected to choose some air pollution problem, identify a chemical component that is required to help characterize the problem, and discuss a modern technique that could be used to treat the pollution. The emphasis of the paper should be on presenting a clear understanding of the environmental problem and the treatment technique.Organization: The following is a suggested outline that can be used for the paper.l Introduction- set up environmental issue and analytical techniques employe.l Treatment techniques- principles only. Include working principles, avoid detailed procedures, comparison of procedures if appropriate, advantages/disadvantages, etc.l Application to environmental issue- include real world data, summary of results quality of data etc.教师评语：教师签字： 年 月 日1. IntroductionFrom July 24 to Aug 8,2015, Shanghai had been suffering from ozone pollution for 11 days in row. Data from the Shanghai Environment Monitoring Center shows ozone pollution has been the primary pollutant in the city from July 24 to August 4. The most polluted day was August 4, when the air quality index (AQI) surged to 181.As the main photochemically produced atmospheric constituent, surface ozone (O3) is a major pollutant that can cause serious damage to human health and ecological environment. Surface ozone is formed in the air as a result of complex photochemical reactions involving nitrogen oxides (NO + NO = NOx), carbon monoxide (CO), and various volatile organic compounds (VOCs), which mostly result from anthropogenic activities. The temporal variations of surface ozone have been widely studied for several decades. Many studies indicated that the temporal variations of ozone concentration have distinct regional characteristics.Chief forecaster from the Shanghai Environment Monitoring Center, Duan Yusen, explained that ozone pollution is a result of air pollution from automobile exhaust and industrial emissions; under high temperature and sunny conditions, such as the summer days in Shanghai, nitrogen oxide gases and volatile organic compounds react chemically to form ozone.Ozone protects people from ultraviolet rays if it is up in the atmosphere. However, peoples health is severely threatened by close exposure to ozone. Potential symptoms arising from prolonged exposure to ozone include respiratory diseases, coughing and damage to the immune system.Breathing masks cannot prevent ozone pollution. Environmental departments advise people to avoid outdoor activities when the pollution is the most severe between 2 to 3 oclock in the afternoon. Ozone pollution is naturally relieved in September.Shanghai, situated on the east coast of China, is a metropolis with a total population over 24 million as of 2013. The rapid growing urbanization causes wide-ranging consequences for the environment. One of the most serious environmental problems is the enhanced ozone concentration in Shanghai, so it is vital and urgent to gain a good understanding of ozone production in Shanghai.2. Ozone basicsOzone is a gas composed of three atoms of oxygen (O3). Ozone occurs both in the Earths upper atmosphere and at ground level. Ozone can be good or bad, depending on where it is found.Called stratospheric ozone, good ozone occurs naturally in the upper atmosphere, where it forms a protective layer that shields us from the suns harmful ultraviolet rays. This beneficial ozone has been partially destroyed by manmade chemicals, causing what is sometimes called a hole in the ozone. The good news is, this hole is diminishing.Tropospheric, or ground level ozone, is not emitted directly into the air, but is created by chemical reactions between oxides of nitrogen (NOx) and volatile organic compounds (VOC). This happens when pollutants emitted by cars, power plants, industrial boilers, refineries, chemical plants, and other sources chemically react in the presence of sunlight. Ozone at ground level is a harmful air pollutant, because of its effects on people and the environment, and it is the main ingredient in “smog.Ozone is most likely to reach unhealthy levels on hot sunny days in urban environments, but can still reach high levels during colder months. Ozone can also be transported long distances by wind, so even rural areas can experience high ozone levels.Ozone in the air we breathe can harm our health. People most at risk from breathing air containing ozone include people with asthma, children, older adults, and people who are active outdoors, especially outdoor workers. In addition, people with certain genetic characteristics, and people with reduced intake of certain nutrients, such as vitamins C and E, are at greater risk from ozone exposure. Breathing ozone can trigger a variety of health problems including chest pain, coughing, throat irritation, and airway inflammation. It also can reduce lung function and harm lung tissue. Ozone can worsen bronchitis, emphysema, and asthma, leading to increased medical care.3. Where Does Ozone Come FromUnlike many other pollutants, ozone is not introduced directly to the air by man or nature, but forms in the air by chemical reaction. The compounds called precursors, that eventually react to form ozone may be natural constituents of the atmosphere (as are oxygen and nitrogen), may be introduced directly as pollutants, or may be formed (as is ozone itself) by chemical reaction.High in the upper atmosphere, large amounts of ozone are produced by sunlight from the oxygen present in the air. Near the ground, ozone is produced primarily from man-made compounds. While many different compounds are involved, two basic precursor classes control the ozone production process: volatile organic compounds( VOC) and oxides of nitrogen (NOx).VOC enters the air from a variety of human activities , among them fossil fuel combustion (primarily in auto exhaust), chemical processing , fuel storage and handling and solvent usage (such as painting or degreasing). VOC also enter the air from natural sources, such as biological decay and the vegetative growth process. Oxides of nitrogen, a component in the photochemical process, is primarily emitted to the atmosphere from the burning of fuels.Because the air moves readily from one location to another, the air we breathe at a given place and time will contain ozone from natural las well as man-made sources. Measurements have shown, however, that ozone concentrations in and near large urban centers where man-made sources predominate, are frequently far greater than concentrations in remote locations unaffected by human activity. These measurements; coupled with a variety of theoretical studies, point to human activityespecially that concentrated in large urban centersas the source of primary concern. Control of emissions of ozone precursors associated with human activity will be instrumental in achieving the ozone standard throughout the world.Ultraviolet radiation from sunlight is required for the photochemical process. Ozone episodes therefore occur typically on sunny days in spring, summer, and fall ,when the sun is high enough to provide sufficient ultraviolent radiation. On cloudy days and during the winter months, ozone levels rarely exceed the standard. Sluggish air movement aids in ozone production by allowing air parcels to remain longer over the source areas and permitting large amounts of precursors to accumulate and ozone to form. Temperature inversions frequently trap the pollutants near the ground. Warm temperatures have always been associated with ozone episodes, although the precise role of temperature in ozone production has not been adequately defined.4. Analytical techniques Shanghai sits on the Yangtze River Delta on Chinas eastern coast and faces the East China Sea, which covers an area of 6340.5 km2. It is located on a peninsula between the Yangtze and Hangzhou Bay, as well as Chongming Island and a number of smaller islands. It is in the subtropics and is under the influence of the summer and winter Asian monsoons. From mid-June to early or mid-July, the meiyu rainy season occurs in Shanghai, with increased precipitation and cloud cover, and decreased sunshine. A summary of the monthly means of the Shanghai surface meteorological variables is given in Table 1. Shanghai is one of the most industrialized cities with the largest adjacent metropolitan areas in the world. Shanghai also suffered from industrial and automobile pollutant emissions. Until 2013, there are more than 2.7 million automobiles in Shanghai.Previous studies on the temporal variations of ozone in Shanghai mainly focused on the diurnal and seasonal cycles, and there is a lack of understanding of the various periodic variations of ozone at other time scales and the possible reasons for these variations. According to the paper Multi-year ozone concentration and its spectra in Shanghai, China, it employs multi-year ozone data from five monitoring stations across the Greater Shanghai area to analyze periodic variations in ozone, the temporal variation of the periods and the difference between different site locations using spectral and wavelet analysis methods.The five monitoring sites in this study are selected to represent different environmental conditions. The easternmost site, Dongtan, is located in an ecological area on Chongming Island. Baoshan is located north of Shanghai in a large steel industrial area. Pudong is located in a suburb and close to a large city park. Down town Xujiahui is a business and human activity center with serious traffic and air pollution problems. Jinshan is located south of Shanghai in a large petrochemical complex. Details of the ozone monitoring stations are shown in Table 2. All monitoring instruments are located on top of tall buildings at least 15 m off the ground. The observations at Baoshan, Pudong, Xujiahui and Jinshan are from January 2006 to December 2012 and at Dongtan from January 2008 to December 2012. At the Dongtan site, UV radiation is also measured data from January 2009 to December 2012.Ozone concentration is measured using an EC9810 Ozone Analyzer (Ecotech, Australia) at all five sites and a photometer is used to measure UV at the Dongtan site. The ozone instrument is automatically set to zero and includes an optional external valve manifold and external calibration sources. The instrument meets the technical specifications of the US Environmental Protection Agency (EPA). Quality control checks are performed every three days including the section of the shelter and instruments as well as zero, precision and span checks. The filter is replaced once in every two weeks and the instrument is calibrated monthly. The O3 concentration is recorded every minute. UV radiation is measured with UV-S-AB-T radiometers (KIPP&ZONEN, The Netherlands) and recorded every minute.The ozone time series at each station are analyzed using the continuous wavelet transform technique. This technique decomposes a time series using a basis function localized in frequency and time (Hsu et al., 2006). The average of each time series is removed and normalized by its standard deviation. Regarding the choice of basis functions for the wavelets, the surface ozone concentrations have clear diurnal and semi-diurnal cycles in the time domain, so a localized wave-like basis function is appropriate. Our approach follows those of Torrence and Compo (1998) and Kestin et al. (1998). Similar method was used in the study of Hsu et al. (2011) to analyze the periodic properties of chemical species.The information of ozone monitoring sites in ShanghaiStationLongitude and latitudeEnvironmental propertiesXujiahuiE121.26, N31.12Downtown area of Shanghai, business and human activities centerJinshanE121.10, N30.54Suburb, a big complex of petrolic-chemical industrial zoneDongtanE121.58, N31.32On the Zhongming island, an ecological areaPudongE121.32, N31.14Sub urban area, close to a large city parkBaoshanE121.27, N31.24Suburb, a big complex of steel industrial zone5. ResultsAnalysis of observed ozone data in 2006 from five monitoring sites (Xujiahui, Chongming, Baoshan, Pudong, Jinshan) in Shanghai reveals that ozone (O-3) concentrations in Xujiahui are higher at weekends than those on weekdays, despite the fact that emissions of ozone precursor substances, such as oxides of nitrogen (NOx ), carbon monoxide (CO) and volatile organic compounds (VOCs) are lower at weekends than those on weekdays. The possible chemical cause of ozone weekend effect is that NO2/NO ratio increases at weekends by 25.61% compared with those on weekdays. In addition, because of an average 12.13% reduction in NO (x) (NO NO2) in the early morning (05:00-09:00) at weekends compared with that on weekdays, the ozone inhibition period ends 0.5 h earlier at weekends resulting in the longer duration of ozone accumulation and the higher ozone production rate. The rate of ozone production is a function of VOCs and NO (x) in the atmosphere. VOCs/NOx ratio in Xujiahui is 4.55 at weekends, and 4.37 on weekdays, belonging to the NOx-limited. The increasing VOCs/NOx ratio at weekends leads to ozone enhancement from 73 ppbv to 80 ppbv, which are consistent with ozone weekend effect in Xujiahui. Furthermore, combining with MICAPS cloud amount data, the fact that ozone weekend effect in Xujiahui weakens gradually along with the increasing of cloud amount indicates that ozone photochemical production leads to ozone weekend effect in Xujiahui of Shanghai.Several studies suggested that emissions of NOx, CO, and VOCs are different between weekdays (MondayFriday) and weekend (Saturday and Sunday) due to different traffic and industrial activities between weekend and weekday ( Cleveland et al., 1974, Lebron, 1975 and Qin et al., 2004). As a result, O3 concentrations are different between weekend and weekday because the change of emission inventories of O3 precursors. This phenomenon has caused general interests because the weekend effect presents a result of “natural atmospheric experiment” for O3 formation study. The weekend effects on O3 concentrations are different in various cities. If O3 formation is under NOx-sensitive regime, the reduction of NOx emissions will lead to decrease in O3 concentrations. However, if O3 formation is under VOC-sensitive regime, the reduction of NOx emissions will lead to increase in O3 concentrations. In this study, the weekend effects will give insights whether the O3 formation is under NOx-sensitive or VOC-sensitive regime in the city of Shanghai.Fig.1 Diurnal variation of O3 concentrations and NO2/NOFig.2 Model calculation of O3 sensitivity to NOx changes(upper panel),O3 sensitivity to total VOC changes (middle panel), and O3 sensitivity to solo aromatic changes (lower panel).Fig. 4 shows the differences between weekend and weekday for O3, NO, and NO2 concentrations. The result suggests that the O3 concentrations are higher during weekend than weekday. The maximum O3 weekend enhancement is about 4 ppbv at noontime. By contrast, the NO, and NO2 concentrations are lower during weekend than weekday due to less traffic and industrial activities. The maximum weekend decrease for NO is at morning, indicating that the smaller emissions of NO due to less traffic during weekend. During daytime, the NO2 concentrations are consistently lower during weekend than weekday. As a result, the large reduction in the daytime NO2 concentrations produces enhancements in OH concentrations, resulting in higher O3 production during weekend. This result suggests that in the city of Shanghai, the O3 formation is clearly under VOC-sensitive regime. This result is consistent to a modeling study in a companion paper. In the study, the ratio of CH2O/NOY is calculated by using a regional chemical/dynamical model. The calculated ratio is much less than 0.28 in the Shanghai region, which indicates that in the Shanghai region, the O3 production is under VOC-sensitive regime as suggested by Sillman (1995). This conclusion is further supported by the changes of VOC concentrations during weekend. Fig. 10 shows that the VOC concentrations are generally decreased during weekend, especially for aromatics which have high OH reactivities. This decrease in VOC produces some off-set effect for the O3 increase during weekend under VOC-sensitive regime. For example, the NCAR-MM2 model calculation suggests that: (1) if only the reduction in NOx emission is considered, O3 concentrations could increase by 9 ppbv in noontime (2) if both reductions in NOx and VOC emissions are considered, O3 concentrations could increase by 5 ppbv in noontime. The late case is consistent with the measured result, and also suggests that the enhancement in O3 concentrations is mainly due to the decrease in NOx emissions.Fig.3 Measured monthly averaged VOC concentrations at the urban site, including alkanes, alkenes, aromatics, alcohols, aldehydes, and ketones.From the weekend effect study, we conclude that the O3 formation in the city of Shanghai is under VOC-sensitive regime. In order to better understand the O3 formation under different NOx and VOC conditions, a sensitivity study is conducted by applying the NCAR-MM model to study sensitivity of O3 concentrations to various NOx and VOC conditions. The initial conditions of the base run of the model are: H2O, CH4, and CO mixing ratios are equal to 0.02, 2, and 1 ppmv, respectively. There are 10 case runs in which NOx concentrations vary from 35 to 130