Photochemical dispersion modeling: Review of model concepts and applications studies

Over the last decade, the development and application of sophisticated atmospheric models that simulate the transport and dispersion of ozone and its precursors have advanced rapidly. Further advancements are most likely to be found in more complete temporal and spatial characterization of photochemical smog formation processes via measurement. This paper provides an overview of the development of atmospheric photochemical dispersion models, first discussing in general terms the various physical processes occurring in the atmosphere that govern the formation, transport, and ultimate fate of ozone. Procedures for representing these physical processes in mathematical terms are presented next. Nearly all of the photochemical models in use today are derived from the semiempirical atmospheric diffusion equation, though theoretical formulations vary depending on which of the various terms in the pollutant mass balance equation are deemed significant for the application at hand. Examples of recent applications of the range of available photochemical model are presented, together with estimates of the accuracy of each generic modeling concept. Several topics warranting future research are identified, including the need to incorporate explicitly more of the stochastic (or probabilistic) nature of the atmosphere into the form of current photochemical model predictions (i.e., estimates of the variance and higher order moments of the predicted concentration distribution).     

Air pollution in the semitropical Saudi urban area

This paper presents the outcome of research conducted in the city of Jeddah, Saudi Arabia. Analysis of recorded meteorological elements shows that the atmosphere of the area favors the accumulation of air pollutants. Dustfall rates were measured at 22 stations in different districts. High rates of dustfall were found in all districts, with maximum recorded values in central urban and industrial districts. Collected samples were analyzed to determine the causes of these excessive precipitations. Suspended particulate matter and other pollutants were found to exceed air quality standards set to meet environmental requirements. Carbon monoxide was found to exceed the air quality standard of 9 μL/L. Concentrations of photochemical oxidants indicated the possibility of Los Angeles-type photochemical smog formation. Geographic distribution of pollutant concentrations and chemical constituents of particulates were found to be influenced by both manmade and natural causes. Results are discussed and several conclusions are given.     

The design considerations for ozone and acid aerosol exposure and health investigations: The fairview lake summer camp — Photochemical smog case study

The health effects associated with ozone and acidic particulate sulfate exposures to active children have been and are being addressed in field epidemiological studies at summar camps in rural areas of the Northeastern U.S. The rationale and study design for studies, which have been conducted in Pennsylvania and New Jersey, are developed and reviewed. As background, results are summarized for human clinical and epidemiological studies and animal studies. These provided the basis for selection of health outcomes measured results from chemical characterization and transport studies are reviewed to define the criteria used for selection of a site which is effected by high ozone and acid species during photochemical smog episodes. The integration of the study design is discussed in detail by reviewing it application to the 1984 — Fairview Lake Camp Study (July 8 to August 4). The features of the camp study are reviewed, including the study population, pulmonary function procedures and analyses, air pollution monitoring instrumentation, and the site characteristics. The pollution exposure data are presented, for ozone and acidic sulfates and examined for the range and distribution concentration. Further information is provided on the intensity and duration of episodes encountered over the course of the study. Episodes occurred which had ozone and acid sulfates, ozone alone, and acid sulfates alone.     

治理长江上游水土流失的对策

作为一个发展中国家,中国除了由工业污染造成的臭氧层破坏、酸雨、光化学烟雾等环境问题之外。还有水土流失、沙漠化、森林植被减少等所谓的“欠发达的环境问题”。近年来,长江上游的水土流失问题十分严重,不仅成为长江下游洪涝灾害的址接原因,而且还然及整个长江流域的可持续发展。为了加快长江上游水土流失治理的进程,本文提出政府要从制度创新、加强组织体系建设、宣传可持续发展的新观念等多方面入手,进行全面综合治理。     

A model of ozone production in urban plumes

A model of rural smogs and urban plumes introduced into rural smog is developed. The single day variation of level of reactive species including ozone in rural smog in the eastern United States is simulated by mathematical modelling. Rural air masses are modelled as though they were outdoor smog chamber systems of low inital contaminant concentration to which small additional injections of contaminants, representing rural emissions, are made throughout the day. Rural smogs containing urban plumes are modelled as though they were outdoor inflatable smog chambers to which relatively large amounts of pollution material are added in the early minutes after sunrise and which are continuously diluted with material from chambers simulating rural smog. The urban plume model is specifically intended to simulate the photochemistry of parcels of air which sweep over relatively isolated cities in the eastern United States.The model runs suggest that the observed lack of urban plumes downwind of small cities is due to dilution. Additionally, the model suggests that the concentrations of both ozone and ozone precursors in rural smog have a significant effect on ozone production in urban plumes.     

The chemistry of smog formation: A review of current knowledge

This paper describes smog chemistry and the methods used to develop our knowledge of its complex chemistry. These methods employ computer modeling, fundamental chemistry, smog chamber experiments, sophisticated analytical instrumentation, and process analysis techniques. The photochemistry leading to smog formation involves a kinetically controlled and coupled competitive process. The essential pathway for formation of nitrogen oxides starts with emissions composed primarily of NO, which are converted to NO₂, mostly via reactions with peroxy radicals; NO₂ is converted to photochemically inert nitric acid primarily by reaction with OH. Organics in smog chemistry are eventually oxidized to CO₂ and water; before this, they typically react with OH to form peroxy radicals. The peroxy (RO₂·) radicals couple the organic and nitrogen chemistry by converting NO to NO₂; the RO₂· radicals are converted to RO radicals, which typically lead to oxygenated intermediate organics that continue through OH·---RO₂·---RO· cycles. These OH·---RO₂·---RO· cycles produce CO, CO₂, and radical products. The radical products, which usually derive from photolysis of oxygenated intermediate organic products, are central to the overall process of smog formation. This is because the balance of these radicals affects the rapidity and severity of smog development. The radical balance is, in turn, controlled by the sources and sinks that depend on the HC/NO_x ratio, the types of organics, and the light flux. With only a rudimentary understanding of smog chemistry as a process, many of the effects observed from precursor controls can be explained and the basic shape of Empirical Kinetics Modeling Approach (EKMA) isopleth curves can be accounted for. The next step beyond this basic level of understanding involves a host of subprocesses composed of a complex series of chemical reactions. Current research in smog chemistry centers on the assessment and elucidation of these complex subprocesses. Atmospheric models currently in use rely on condensed chemical mechanisms. All such modern mechanisms treat the same basic processes, but differ both in their method of condensation and in their manner of addressing the complex subprocesses of smog chemistry.     

经济集聚对雾霾污染影响的空间计量研究——以长江三角洲地区为例

雾霾污染是困扰中国经济发展的重大民生与环境问题。基于改进产出密度模型,运用地统计和空间计量模型分析长三角城市2015~2017年雾霾污染空间格局和影响因素。研究发现：（1）雾霾污染存在季节性变化特征并且各城市雾霾污染状况逐渐好转。（2）雾霾污染具有显著的局域集聚特征和空间异质性,杭州、宁波和台州呈现低－低集聚特征,而滁州、扬州、镇江和泰州为高－高集聚型,污染区域集中于省界处,污染程度自西北向东南逐渐降低。雾霾污染存在显著的城际空间正相关和空间溢出效应,周边城市雾霾污染对本地区会产生负影响。（3）长三角城市人口集聚、研发投入、产业结构、工业烟粉尘排放及城市建设均对雾霾污染产生正向影响,对外开放、能源消耗以及降水等因素对雾霾污染产生负向影响;雾霾污染与经济增长之间不存在库兹涅茨曲线关系。经济集聚通过优化生产要素的空间分布与组合、共享治污基础设施等,形成雾霾污染抑制作用。     

Man-made and natural smog in California

The radiocarbon content in creosote bush in the greater Los Angeles area has been found to reflect the distribution of smog. Indications are that smog in the even larger air basin of the San Joaquin Valley of California may be caused in part by recent biospheric emissions rather than by fossil fuel combustion alone.     

Health effects of oxidants

Oxidants of significance to human health include ozone, nitrogen dioxide, and peroxyacetylnitrate. All of these compounds are involved in complex photochemical reactions which makes quantification and prediction of their individual health effects difficult. Ozone causes trauma to lung tissues and interferes with enzyme systems in the lungs and other tissues causing a broad range of symptoms. Measurable health impacts can occur at concentrations as low as 390 μg/m³. Acute effects of ozone exposure are reversible at normal urban concentrations (80–120 μg/m³). A special problem of concern, however, is increased susceptibility to infectious diseases contracted through the lungs. Nitrogen dioxide also causes trauma to lung tissues and interferes with enzyme systems. Measurable impacts can occur at concentrations as low as 100 μg/m³, but recovery is rapid and it is not known whether repeated exposures at this level have cumulative effects or predispose the lungs to permanent damage. Chronic exposure of laboratory animals to higher nitrogen dioxide levels can cause emphysema-like conditions and reduction in resistance to respiratory infection. Epidemiological studies of children in houses with gas stoves confirm the finding of reduced resistance to respiratory infection. The U.S. EPA estimates that health effects may occur in young children exposed to concentrations in excess of 280 to 560 μg/m³ one-hour average. These concentrations occur routinely in houses having gas stoves. Peroxyacetylnitrate is a powerful eye irritant in photochemical smog. Other health effects are similar to those of ozone, but less important because of the relatively low concentrations of this pollutant compared to other oxidants.     

Photochemical smog effects in mixed conifer forests along a natural gradient of ozone and nitrogen deposition in the San Bernardino Mountains

Toxic effects of photochemical smog on ponderosa and Jeffrey pines in the San Bernardino Mountains were discovered in the 1950s. It was revealed that ozone is the main cause of foliar injury manifested as chlorotic mottle and premature needle senescence. Various morphological, physiological and biochemical alterations in the affected plants have been reported over a period of about 40 years of multidisciplinary research. Recently, the focus of research has shifted from studying the effects of ozone to multiple pollutant effects. Recent studies have indicated that the combination of ozone and nitrogen may alter biomass allocation in pines towards that of deciduous trees, accelerate litter accumulation, and increase carbon sequestration rates in heavily polluted forests. Further study of the effects of multiple pollutants, and their long-term consequences on the mixed conifer ecosystem, cannot be adequately done using the original San Bernardino Mountains Air Pollution Gradient network. To correct deficiencies in the design, the new site network is being configured for long-term studies on multiple air pollutant concentrations and deposition, physiological and biochemical changes in trees, growth and composition of over-story species, biogeochemical cycling including carbon cycling and sequestration, water quality, and biodiversity of forest ecosystems. Eleven sites have been re-established. A comparison of 1974 stand composition with data from 2000 stand composition indicate that significant changes in species composition have occurred at some sites with less change at other sites. Moist, high-pollution sites have experienced the greatest amount of forest change, while dryer low-pollution sites have experienced the least amount of stand change. In general, ponderosa pine had the lowest basal area increases and the highest mortality across the San Bernardino Mountains.     

Air quality modeling for Houston-Galveston-Brazoria area

A coupled numerical model of the atmospheric thermo-hydrodynamics and pollutant photochemical transport is described. This model can be used to study the complex relationships between the chemical and thermo-hydrodynamic processes in the atmosphere of urban areas with an emphasis on photochemical ozone formation. Preliminary numerical results of ozone and other key chemical atmospheric pollutant concentrations and distribution across the Houston-Galveston-Brazoria area using virtual emission data from area and mobile sources are presented.     

Mechanistic aspects regarding the direct aqueous environmental photochemistry of phenol and its simple halogenated derivatives. A review

We have reviewed the mechanistic aspects regarding the direct aqueous phase environmental photochemistry of phenol and its simple halogenated derivatives. These compounds are important industrial and natural products, are ubiquitous in aquatic systems, and their acute and chronic toxicity makes their environmental fate of interest. Work over the past two decades has unified the photochemistry of phenol and its simple halogenated derivatives. In general, three photochemical pathways dominate in aqueous solution depending on the nature of the substrate: (1) photoionization, (2) photochemical aryl-halogen bond homolysis, and (3) photochemical aryl-halogen bond heterolysis. Photoionization typically results in an array of biaryl radical coupling products which are only relevant for highly concentrated waste streams. Photolytic aryl-halogen bond homolysis will primarily give photoreduction products where reducing agents such as dissolved organic matter or reduced metal cations are present, and radical coupling products in highly concentrated waste streams. The 2- and 4-substituted halophenols may undergo photochemical aryl-halogen bond heterolysis upon irradiation to give an aryl cation. The aryl cation can be attacked by water to give the corresponding hydroxylated derivative, or may deprotonate to generate alpha- and gamma-ketocarbenes, respectively. Following their formation, the singlet alpha-ketocarbenes may undergo Wolff rearrangements to cyclopentadiene-ketenes that are subsequently hydrolyzed to cyclopentadiene carboxylic acids. The triplet alpha- and gamma-ketocarbenes are attacked by oxygen and hydrolyzed to give benzoquinones, directly hydrolyzed to yield hydroquinones, reduced to give phenols, or could take part in coupling reactions in highly concentrated waste streams to give dimers and hydroxybiaryl complexes. Additional studies in natural water samples are required to assess the relative importance of these direct irradiation mechanisms relative to indirect photolysis and other abiotic and biotic degradation and environmental partitioning pathways across the continuum of marine, freshwater, and wastewater biogeochemical signatures.     

Existing oxidant/ozone standards in OECD countries

This paper describes the historical development and current legislation to control photochemical oxidant pollution in OECD countries. Policies for implementing, attaining, and maintaining ambient air quality standards or goals are discussed, problems associated with the various steps are highlighted, and the possibility of international policy guidelines which could control pollution across national frontiers is considered. To date, only a few countries have formulated ambient air quality standards for ozone/ oxidants; these standards are usually short-term averages over 1 h, ranging from 0.06 ppm (μL/L) in Japan to 0.12 ppm (μL/L) in the United States. The current interest in air quality management on an international scale leads to the conclusion that successful control of photochemical oxidant pollution would be best accomplished through the establishment of internationally acceptable standards or goals for oxidants/ozone based on health effects and other relevant environmental impacts, in combination with control strategies developed and implemented on an international level.     

Characterizing the PM2.5-related health benefits of emission reductions for 17 industrial,area and mobile emission sectors across the U.S.

BackgroundAir pollution benefits assessments tend to be time and resource intensive. Reduced-form approaches offer computational efficiency, but may introduce uncertainty. Some reduced-form approaches apply simplified air quality models, which may not capture the complex non-linear chemistry governing the formation of certain pollutants such as PM_2.5. Other approaches apply the results of sophisticated photochemical modeling, but characterize only a small number of source types in a limited geographic area.MethodsWe apply CAMx source apportionment photochemical modeling, coupled with a PC-based human health benefits software program, to develop a suite of PM_2.5 benefit per ton estimates. These per-ton estimates relate emission changes to health impacts and monetized benefits for 17 sectors across the continental U.S., including Electricity Generating Units (EGU), mobile, area and industrial point sources.ResultsThe benefit per ton of reducing directly emitted PM_2.5 is about an order of magnitude larger than reducing emissions of PM_2.5 precursor emissions. On a per-ton basis, the value of reducing directly emitted PM_2.5 and PM_2.5 precursors in 2005 ranges between approximately $1300 (2010$) for reducing a ton of NO_x from Ocean-Going Vessels to about $450,000 (2010$) for reducing a ton of directly emitted PM_2.5 from Iron and Steel facilities. The benefit per ton estimates for 2016 are generally higher than the 2005 estimates. The values estimated here are generally comparable with those generated using photochemical modeling, but larger than those calculated using simplified air quality models.ConclusionsOur approach characterizes well the per-ton benefits of reducing emissions from a broad array of 17 industrial point, EGU and mobile sectors, while our use of photochemical air quality modeling gives us greater confidence that we have accounted for the non-linear chemistry governing PM_2.5 formation. The resulting benefit per-ton estimates thus represent a compromise between approaches that may simplify the treatment of PM_2.5 air quality formation and those techniques that are based in photochemical modeling but account for only a small number of emission sources.     

户用沼气模式生命周期减排清单与环境效益分析

相对于传统农业活动,以沼气为纽带的生态农业生产具有清洁的能源生产和高度闭环的废物回收处置等明显优势,在全国范围内得到入户推广。本文综合考虑沼气工程建造、使用和综合利用等生命周期过程,分析了典型户用沼气池综合利用各阶段环境节能减排清单,并在此基础上评价其环境效益。结果表明,"猪-沼-稻-果"综合农业利用模式下单位沼气池节能减排效果明显,其中CO2、PM10、CH4和CO净减排量分别达3 060.700kg、19.820kg、12.960kg和75.590kg,总净节能达9 068.4MJ。其中,玉米秸秆、沼液沼渣的利用和燃煤替代对温室效应的减缓明显,畜禽粪便的利用和燃煤的替代减缓了环境酸化以及富营养化过程,而光化学氧化的减缓主要来自玉米秸秆的利用而减少的CO、VOC的排放,沼气工程对人体毒害的减缓主要是来自燃煤替代而减少的SO2和PM10排放。户用沼气利用对各种环境影响均有减缓作用,其中对光化学氧化、富营养化、环境酸化和温室效应的改善最为显著,对于降低能源耗竭、减缓对人体的毒性也起到了较好的作用。     

The Impact of Perceptual and Situational Factors on Environmental Communication: A Study of Citizen Engagement in China

This study applied a situational approach to understanding an environmental problem: PM2.5 (its resulted haze and smog air pollution) in China. Based on a national sample of 374 citizens living in China, it tested a situational model of problem solving and extended it by adding citizens’ environmental engagement behaviour as an immediate consequence of their communicative action. Results of a structural equation modelling analysis supported all the causal links in the conceptual model. Moreover, communicative action significantly mediated the relationship between referent criterion and environmental engagement. Problem recognition, constraint recognition, and involvement recognition did not influence environmental engagement directly, but exerted their significant indirect impact via two key mediators in the model: situational motivation in problem solving and communicative action in problem solving. Theoretical and practical implications of the present study were discussed.     

Life cycle assessment part 2: current impact assessment practice

Providing our society with goods and services contributes to a wide range of environmental impacts. Waste generation, emissions and the consumption of resources occur at many stages in a product's life cycle-from raw material extraction, energy acquisition, production and manufacturing, use, reuse, recycling, through to ultimate disposal. These all contribute to impacts such as climate change, stratospheric ozone depletion, photooxidant formation (smog), eutrophication, acidification, toxicological stress on human health and ecosystems, the depletion of resources and noise-among others. The need exists to address these product-related contributions more holistically and in an integrated manner, providing complimentary insights to those of regulatory/process-oriented methodologies. A previous article (Part 1, Rebitzer et al., 2004) outlined how to define and model a product's life cycle in current practice, as well as the methods and tools that are available for compiling the associated waste, emissions and resource consumption data into a life cycle inventory. This article highlights how practitioners and researchers from many domains have come together to provide indicators for the different impacts attributable to products in the life cycle impact assessment (LCIA) phase of life cycle assessment (LCA).     

Traffic and outdoor air pollution levels near highways in Baghdad,Iraq

In Iraq, the number of passenger cars, trucks and buses, local generators, and heavy construction equipment rose to a considerable extent since 2003, causing high environmental problems. Many types of pollutants were monitored and recorded for 24 h during March 2016. The study attempts to explore and establish a relationship between the volume of activity and the movement of motor vehicles of various compounds and contaminants resulting from their exhaust pipes, such as sulfur dioxide, particulate matters, oxides of nitrogen, VOCs, and unburned hydrocarbons. The study focused in and around Mohammad Al-Qasim highway adjacent to the University of Technology, Baghdad. The results showed the need for urgent treatments addressed by the environmental authorities in the city. The study results demonstrated that these contaminants are increased during periods of the beginning and end of working hours for government departments. Some types of sulfur compounds (H₂S and SO₂) concentrations were at serious health-threatening levels, which is a result of the high sulfur content in the Iraqi fuel. The concentrations of NOx and VOC were high, also, which could make the studied area vulnerable to the risk of smog formation. The Iraqi government should make greater efforts to protect the environment and human in this country from the transportation pollution risks.     

Levels of polybrominated diphenyl ethers (PBDEs) in dust from personal automobiles in conjunction with studies on the photochemical degradation of decabromodiphenyl ether (BDE-209)

The levels of 21 PBDE congeners were detemined in the dust sampled from 66 personal automobiles. The dominant congener in automobile dust was BDE-209 with a median level of 8.12 μg g?1. Personal vehicle dust samples contained the characteristic profile of the PBDE congeners that comprise the PentaBDE and DecaBDE commercial formulations. Levels of PBDEs in personal automobiles are generally reduced in comparison to our previously reported levels in resale vehicles on dealership lots presumably due to a dilution effect introduced by dust or debris that does not originate from the vehicle. Laboratory photochemical studies were conducted on both automobile dust collected from personal vehicles as well as BDE-209 adsorbed to sodium sulfate. No significant degradation occurred in the personal vehicle dust after 56 days of constant UVA irradiation while significant degradation did occur with BDE-209 adsorbed to sodium sulfate. PBDEs from the degradation of BDE-209 were identified and potential degradation pathways elucidated. Human exposure potential to PBDEs from automobile dust ingestion remains a serious concern in the U.S. population.