The Association between Ambient Air Pollution and Daily Mortality in Beijing after the 2008 Olympics: A Time Series Study

In recent decades, ambient air pollution has been an important public health issue in Beijing, but little is known about air pollution and health effects after the 2008 Beijing Olympics. We conduct a time-series analysis to evaluate associations between daily mortality (nonaccidental, cardiovascular and respiratory mortality) and the major air pollutants (carbon monoxide, nitrogen dioxide and particulate matter less than 10 µm in aerodynamic diameter) in Beijing during the two years (2009∼2010) after the 2008 Beijing Olympics. We used generalized additive model to analyze relationship between daily mortality and air pollution. In single air pollutant model with two-day moving average concentrations of the air pollutants, increase in their interquartile range (IQR) associated with percent increase in nonaccidental mortality, 2.55 percent [95% confidence interval (CI): 1.99, 3.11] for CO, 2.54 percent (95% CI: 2.00, 3.08) for NO₂ and 1.80 percent (95% CI: 1.21, 2.40) for PM₁₀, respectively; increases in the IQR of air pollutant concentrations associated with percent increase in cardiovascular mortality, 2.88 percent (95% CI: 2.10,3.65) for CO, 2.63 percent (95% CI: 1.87, 3.39) for NO₂ and 1.72 percent (95% CI: 0.88, 2.55) for PM₁₀, respectively; and increase in IQR of air pollutant concentrations associated with respiratory mortality, 2.39 percent (95% CI: 0.68, 4.09) for CO, 1.79 percent (95% CI: 0.11, 3.47) for NO₂ and 2.07 percent (95% CI: 0.21, 3.92) for PM₁₀, respectively. We used the principal component analysis to avoid collinearity of varied air pollutants. In addition, the association stratified by sex and age was also examined. Ambient air pollution remained a significant contributor to nonaccidental and cardiopulmonary mortalities in Beijing during 2009∼2010.     

Association between air pollution and acute childhood wheezy episodes: prospective observational study.

OBJECTIVE--To examine the association between the air pollutants ozone, sulphur dioxide, and nitrogen dioxide and the incidence of acute childhood wheezy episodes. DESIGN--Prospective observational study over one year. SETTING--District general hospital. SUBJECTS--1025 children attending the accident and emergency department with acute wheezy episodes; 4285 children with other conditions as the control group. MAIN OUTCOME MEASURES--Daily incidence of acute wheezy episodes. RESULTS--After seasonal adjustment, day to day variations in daily average concentrations of ozone and sulphur dioxide were found to have significant associations with the incidence of acute wheezy episodes. The strongest association was with ozone, for which a non-linear U shaped relation was seen. In terms of the incidence rate ratio (1 at a mean 24 hour ozone concentration of 40 microg/m3 (SD=19.1)), children were more likely to attend when the concentration was two standard deviations below the mean (incidence rate ratio=3.01; 95% confidence interval 2.17 to 4.18) or two standard deviations above the mean (1.34; 1.09 to 1.66). Sulphur dioxide had a weaker log-linear relation with incidence (1.12; 1.05 to 1.19 for each standard deviation (14.1) increase in sulphur dioxide concentration). Further adjustment for temperature and wind speed did not significantly alter these associations. CONCLUSIONS--Independent of season, temperature, and wind speed, fluctuations in concentrations of atmospheric ozone and sulphur dioxide are strongly associated with patterns of attendance at accident and emergency departments for acute childhood wheezy episodes. A critical ozone concentration seems to exist in the atmosphere above or below which children are more likely to develop symptoms.     

Association between Air Pollution and General Outpatient Clinic Consultations for Upper Respiratory Tract Infections in Hong Kong

Background and Objectives

Many studies have shown the adverse effects of air pollution on respiratory health, but few have examined the effects of air pollution on service utilisation in the primary care setting. The aim of this study was to examine the association between air pollution and the daily number of consultations due to upper respiratory tract infections (URTIs) in general outpatient clinics (GOPCs) in Hong Kong.

Methods

Daily data on the numbers of consultations due to URTIs in GOPCs, the concentrations of major air pollutants, and the mean values of metrological variables were retrospectively collected over a 3-year period (2008–2010, inclusive). Generalised additive models were constructed to examine the association between air pollution and the daily number of consultations, and to derive the relative risks and 95% confidence intervals (95% CI) of GOPC consultations for a unit increase in the concentrations of air pollutants.

Results

The mean daily consultations due to URTIs in GOPCs ranged from 68.4 to 253.0 over the study period. The summary relative risks (and 95% CI) of daily consultations in all GOPCs for the air pollutants PM₁₀, NO₂, O₃, and SO₂ were 1.005 (1.002, 1.009), 1.010 (1.006, 1.013), 1.009 (1.006, 1.012), and 1.004 (1.000, 1.008) respectively, per 10 µg/m³ increase in the concentration of each pollutant.

Conclusion

Significant associations were found between the daily number of consultations due to URTIs in GOPCs and the concentrations of air pollutants, implying that air pollution incurs a substantial morbidity and increases the burden of primary health care services.     

Seasonal, daily and intradiurnal variation of PM10, NO2, NO and O3 in residential part of Zagreb, Croatia

Pollutants such as particulate matter, nitrogen oxides, carbon oxides, ground-level ozone, etc. are harmful to human health. Study of pollutant variation and its relationship with both dynamic and thermodynamic atmospheric boundary layer (ABL) structures is of importance not only for environmental protection but also for the public at large. The aim of this study was to analyze seasonal, daily and intradiurnal variation of PM10, NO2, NO and O3 in a residential part of an urban area, and the effect of some meteorological parameters. The study was conducted from January 1 till December 31, 2004 in the City of Zagreb using following methods: beta radiation absorption, chemiluminescence and UV photometry. The results presented in this article, show the dependence of air pollution levels upon traffic density, seasons and meteorological conditions. Considering the level of air pollution relative to the regulated limit and tolerated values, the measured 24-hour concentrations of all study pollutants exceeded the borderline values and/or tolerated values, however, the number of days with such pollutant concentrations did not exceed the allowed frequency. This is a preliminary study with the main objectives to point to the possible identification of the source of pollution and to assess the level of air contamination according to the new national legislation coordinated with European regulations. Future measurements and studies should evaluate in detail the causes of the concentration levels detected.     

The Effect of Elevated Ozone Concentrations with Varying Shading on Dry Matter Loss in a Winter Wheat-Producing Region in China

Surface-level ozone pollution causes crop production loss by directly reducing healthy green leaf area available for carbon fixation. Ozone and its precursors also affect crop photosynthesis indirectly by decreasing solar irradiance. Pollutants are reported to have become even more severe in Eastern China over the last ten years. In this study, we investigated the effect of a combination of elevated ozone concentrations and reduced solar irradiance on a popular winter wheat Yangmai13 (Triticum aestivum L.) at field and regional levels in China. Winter wheat was grown in artificial shading and open-top-chamber environments. Treatment 1 (T1, i.e., 60% shading with an enhanced ozone of 100±9 ppb), Treatment 2 (T2, i.e., 20% shading with an enhanced ozone of 100±9 ppb), and Control Check Treatment (CK, i.e., no shading with an enhanced ozone of 100±9 ppb), with two plots under each, were established to investigate the response of winter wheat under elevated ozone concentrations and varying solar irradiance. At the field level, linear temporal relationships between dry matter loss and cumulative stomatal ozone uptake were first established through a parameterized stomatal-flux model. At the regional level, ozone concentrations and meteorological variables, including solar irradiance, were simulated using the WRF-CMAQ model (i.e., a meteorology and air quality modeling system). These variables were then used to estimate cumulative stomatal ozone uptake for the four major winter wheat-growing provinces. The regional-level cumulative ozone uptake was then used as the independent variable in field data-based regression models to predict dry matter loss over space and time. Field-level results showed that over 85% (T1: R² = 0.85 & T2: R² = 0.89) of variation in dry matter loss was explained by cumulative ozone uptake. Dry matter was reduced by 3.8% in T1 and 2.2% in T2 for each mmol O₃·m^-2 of cumulative ozone uptake. At the regional level, dry matter loss in winter wheat would reach 50% under elevated ozone concentrations and reduced solar irradiance as determined in T1, and 30% under conditions as determined in T2. Results from this study suggest that a combination of elevated ozone concentrations and reduced solar irradiance could result in substantial dry matter loss in the Chinese wheat-growing regions.     

A Historical Overview of the Ozone Exposure Problem

Ozone can be found in essentially all locations in the troposphere. Too much exposure of vegetation and humans to this potent oxidizing gas can prove toxic. Reports of human toxicity to ozone first appeared in the 1800's from accidental occupational exposures when ozone was first discovered. Ozone was recognized as damaging field vegetation with a report of altered leaf morphology in grapes in the 1950s. Ozone is the major oxidant component in photochemical smog, and is produced by reactions of volatile organic compounds and oxides of nitrogen with sunlight present. Soon after the inception of the U.S. Environmental Protection Agency (US EPA), the Agency set a general “oxidants” standard (which included ozone) in 1971. A primary standard was created to protect human health and a secondary standard to protect against agricultural losses, ecological damage, and other losses. Ozone concentrations have decreased steadily over the last two decades in some areas of the U.S., but have increased in other areas. Several aspects of ozone exposure need further characterization, including better determination of rural concentrations and the relationship of outdoor to indoor concentrations. Ozone is one of the six criteria air pollutants requiring a formal reexamination of the new findings of effects on health and vegetation on a periodic basis, a process that leads to the publication of an US EPA criteria document. As a result of further study concerning ozone effects, significant changes were made to pollution standards in 1979 and 1997. This toxicant has remained a major air pollutant of concern in the U.S. despite regulation and intense study over several decades.     

Patterns of understory diversity in mixed coniferous forests of southern California impacted by air pollution

The forests of the San Bernardino Mountains have been subject to ozone and nitrogen (N) deposition for some 60 years. Much work has been done to assess the impacts of these pollutants on trees, but little is known about how the diverse understory flora has fared. Understory vegetation has declined in diversity in response to elevated N in the eastern U.S. and Europe. Six sites along an ozone and N deposition gradient that had been part of a long-term study on response of plants to air pollution beginning in 1973 were resampled in 2003. Historic ozone data and leaf injury scores confirmed the gradient. Present-day ozone levels were almost half of these, and recent atmospheric N pollution concentrations confirmed the continued air pollution gradient. Both total and extractable soil N were higher in sites on the western end of the gradient closer to the urban source of pollution, pH was lower, and soil carbon (C) and litter were higher. The gradient also had decreasing precipitation and increasing elevation from west to east. However, the dominant tree species were the same across the gradient. Tree basal area increased during the 30-year interval in five of the sites. The two westernmost sites had 30-45% cover divided equally between native and exotic understory herbaceous species, while the other sites had only 3-13% cover dominated by native species. The high production is likely related to higher precipitation at the western sites as well as elevated N. The species richness was in the range of 24 to 30 in four of the sites, but one site of intermediate N deposition had 42 species, while the easternmost, least polluted site had 57 species. These were primarily native species, as no site had more than one to three exotic species. In three of six sites, 20-40% of species were lost between 1973 and 2003, including the two westernmost sites. Two sites with intermediate pollution had little change in total species number over 30 years, and the easternmost site had more species in 2003. The easternmost site is also the driest and has the most sunlight filtering to the forest floor, possibly accounting for the higher species richness. The confounding effects of the precipitation gradient and possibly local disturbances do not show a simple correlation of air pollution with patterns of native and invasive species cover and richness. Nevertheless, the decline of native species and dominance by exotic species in the two westernmost polluted sites is cause for concern that air pollution is affecting the understory vegetation adversely.     

Pulmonary expression of preproET-1 and preproET-3 mRNAs is altered reciprocally in rats after inhalation of air pollutants

Perturbation of vascular homeostasis is an important mechanism related to the acute health effects of inhaled pollutants. Inhalation of urban particulate matter and ozone by rats has been shown to result in increased synthesis of the potent vasoactive peptide endothelin (ET)-1 in the lungs, with spillover into the circulation. In the present work, we have analyzed the interrelationships between responses of the three major endothelin isoforms, ET-1[1-21], ET-2[1-21], and ET-3[1-21], to inhaled pollutants at the peptide and gene expression levels. Fisher-344 rats were exposed for 4 hrs by nose-only route to clean air, urban particles EHC-93 (0, 50 mg/m3), ozone (0, 0.8 ppm), or ozone and particles together. Circulating levels of both the ET-1 [1-21] and ET-3[1-21] peptides were increased immediately after exposure to particulate matter or ozone. While expression of preproET-1 mRNA in the lungs increased, expression of preproET-3 mRNA decreased immediately after exposure. PreproET-2 mRNA was not detected in the lungs, and exposure to either pollutant did not affect plasma ET-2 levels. Co-exposure to ozone and particles, while altering lung preproET-1 and preproET-3 mRNA levels in a fashion similar to ozone alone, did not cause changes in the circulating levels of the two corresponding peptides. Thus, de novo synthesis of ET-3 in the lungs is not responsible for the increase of circulating plasma ET-3 after inhalation of pollutants, which implies regulation of preproET-3 at a remote site and, hence, systemic impacts of the pollutants. Upregulation of preproET-1 coupled with down-regulation of preproET-3 in the lungs of animals exposed to air pollutants implies a mismatch of local ET-1/ET(A) receptor-mediated vasoconstriction and ET-3/ET(B) receptor-mediated vasodilation.     

城市植物挥发性有机化合物排放与臭氧相互作用及其机制

近地面臭氧(O₃)已成为继PM_2.5后影响我国空气质量的一种重要二次污染物。随着氮氧化物浓度的持续下降和气候变暖的加剧,城市O₃的形成对挥发性有机化合物的浓度更加敏感。近年来城市绿色空间显著增长,植物源挥发性有机化合物(BVOCs)排放和浓度逐年增加。针对BVOCs与近地面O₃之间复杂的交互作用,从植物BVOCs的特性与作用出发,综述了不同因素尤其是O₃浓度增加对树木生理状态及BVOCs排放速率的影响,定量分析了已有研究中O₃对不同植物异戊二烯和单萜烯排放速率的影响,以及BVOCs对O₃形成的贡献,总结了BVOCs与O₃相互作用研究领域存在的不足。未来亟需加强的研究包括：(1)城市树种BVOCs排放因子的实测,建立物种的排放速率数据库,优化模型参数,提升精细尺度BVOCs排放量估算模型精度;(2)多种环境因子,比如污染物浓度、温湿度等对城市植物BVOCs排放的交互作用和综合影响的研究;(3)植物BVOCs对O     

森林火灾污染物质释放及其影响研究进展

森林火灾是大气中气体污染物和颗粒物的重要来源,可对全球气候系统、大气环境以及生态系统产生重要影响,对全球温室气体和含碳颗粒物释放具有重要的贡献,是推动全球气候变化的重要因素。森林火灾释放污染物已成为区域乃至全球范围内重要污染源之一,这些污染物质与辐射、能见度以及温室效应等问题直接相关。准确地描述森林火灾释放的气体和颗粒污染物释放机理、释放总量、时空分布特征、不同尺度的扩散过程模拟,以及对区域大气环境的影响,对于量化森林火灾释放污染物总量及区域影响具有重要意义。基于森林火灾污染物质释放方面的国内外文献,从火灾释放的污染物质对环境的影响、森林火灾释放污染物定量化和传输路径监测的研究方法、污染物质的扩散和运输模型以及跨区域影响等几个方面进行了综述。森林火灾释放的CO、PM₁₀和PM_2.5对环境和人的生命安全造成巨大威胁,而且森林火灾释放的污染物质能够随气流长距离传输,不仅对当地的空气造成污染,污染物也能够随着气团进行长距离传输,并在传输过程与当地气溶胶混合,形成跨区域污染。森林火灾释放污染物扩散、传输模拟通过不同模型相互耦合完成,包括可燃物载量估算模型、可燃物消耗和释放模型、污染物扩散传输模型,以及污染物预测和可视化模型等。总结了国内外森林火灾释放污染物质主要研究方法,并展望了今后研究重点:目前我国关于森林火灾释放物质相关的研究尚不足以支撑我国森林火灾温室气体释放、污染物释放等方面的研究,并且我国目前还没有发展出适合于我国的森林火灾污染物释放模型,以及污染物扩散、传输系统。森林火灾排放因子库大多数引用国外研究结果,在一定程度上增加不确定性,缺乏森林火灾对区域大气环境影响的定量化研究。因此,今后我国应加强对森林火灾污染物质释放与影响的研究,尤其是污染物质扩散和传输模型的预测和可视化研究以及排放因子的测量。     

Ozone in Spain's national parks and protected forests

In general, it is difficult to measure air pollutant concentrations in remote areas, as they are mostly national parks and protected areas. Passive samplers provide an accurate and inexpensive method for measuring cumulative exposures of different air pollutants. They have been used to collect ozone data in both laboratory and field at different geographical scales. The objective of the present study is to fill the knowledge gap regarding air quality in remote areas of Spain, such as national parks and protected areas. Because there were no systematic data sets on the main air pollutants that could affect these areas, an air quality measurement network was established between 2001 and 2004 on 19 locations inside Spanish national parks and protected areas. The data collected suggest that ozone levels in mountainous areas are high enough to affect sensitive vegetation. Most of the locations registered moderate-to-high ozone levels, with important interannual variability. Altitudinal ozone gradients were observed in most of the parks with complex topography due to the establishment of local circulations that incorporate polluted air masses from polluted airsheds or even long-range transport (i.e., Canary Islands). Different latitude-dependent, yearly cycles were also observed, showing two, one, or no clear peaks depending on the region. These findings extend to the most southerly locations, except in the Canary Islands, where pollution transported from other regions in the upper transport layers probably led to the high concentrations observed.     

Effects of ozone on species composition in an upland grassland

Northern hemispheric background concentrations of ozone are increasing, but few studies have assessed the ecological significance of these changes for grasslands of high conservation value under field conditions. We carried out a 3-year field experiment in which ozone was released at a controlled rate over three experimental transects to produce concentration gradients over the field site, an upland mesotrophic grassland located in the UK. We measured individual species biomass in an annual hay cut in plots receiving ambient ozone, and ambient ozone elevated by mean concentrations of approximately 4 ppb and 10 ppb in the growing seasons of 2008 and 2009. There was a significant negative effect of ozone exposure on herb biomass, but not total grass or legume biomass, in 2008 and 2009. Within the herb fraction, ozone exposure significantly decreased the biomass of Ranunculus species and that of the hemi-parasitic species Rhinanthus minor. Multivariate analysis of species composition, taking into account spatial variation in soil conditions and ozone exposure, showed no significant ozone effect on the grass component. In contrast, by 2009, ozone had become the dominant factor influencing species composition within the combined herb and legume component. Our results suggest that elevated ozone concentrations may be a significant barrier to achieving increased species diversity in managed grasslands.     

Air pollution and gene-specific methylation in the Normative Aging Study: Association,effect modification,and mediation analysis

The mechanisms by which air pollution has multiple systemic effects in humans are not fully elucidated, but appear to include inflammation and thrombosis. This study examines whether concentrations of ozone and components of fine particle mass are associated with changes in methylation on tissue factor (F3), interferon gamma (IFN-γ), interleukin 6 (IL-6), toll-like receptor 2 (TLR-2), and intercellular adhesion molecule 1 (ICAM-1). We investigated associations between air pollution exposure and gene-specific methylation in 777 elderly men participating in the Normative Aging Study (1999–2009). We repeatedly measured methylation at multiple CpG sites within each gene’s promoter region and calculated the mean of the position-specific measurements. We examined intermediate-term associations between primary and secondary air pollutants and mean methylation and methylation at each position with distributed-lag models. Increase in air pollutants concentrations was significantly associated with F3, ICAM-1, and TLR-2 hypomethylation, and IFN-γ and IL-6 hypermethylation. An interquartile range increase in black carbon concentration averaged over the four weeks prior to assessment was associated with a 12% reduction in F3 methylation (95% CI: -17% to -6%). For some genes, the change in methylation was observed only at specific locations within the promoter region. DNA methylation may reflect biological impact of air pollution. We found some significant mediated effects of black carbon on fibrinogen through a decrease in F3 methylation, and of sulfate and ozone on ICAM-1 protein through a decrease in ICAM-1 methylation.     

The effect of air pollutants on physiological processes in plants

Abstract. Important physiological processes, photosynthesis, respiration, carbon allocation and stomatal function are known to be affected by air pollutants. A wide range in sensitivity of photosynthesis both within and between species is evident from the literature for the pollutants sulphur dioxide, ozone, nitrogen oxide and hydrogen fluoride. Some of this variation is clearly due to genetic factors, but much is in response to differences in environmental conditions both prior to and during fumigation. Exposure of plants to mixtures of pollutants generally reduced the threshold at which effects were first detected and increased the level of inhibitory responses. In the majority of studies on stomatal responses to air pollutants, opening occurs at low concentrations, below the threshold for effects on photosynthesis, and closure occurs at injurious concentrations; this latter response often following the inhibition of photosynthesis. Effects on carbon allocation have been reported in response to air pollutants. Changes usually favour leaf development over root growth, which can compensate for a decline in net assimilation rate up to a certain point but may limit water uptake from soils with low moisture content. Future research into physiological effects of air pollutants should incorporate an integrated approach in which both key physiological parameters and growth parameters are measured together with estimates of the effective dose of pollutant. In this way, the underlying mechanisms to changes in growth and development will be more fully understood.     

Predicting tropospheric ozone concentrations in different temporal scales by using multilayer perceptron models

This study encompasses ozone modeling in the lower atmosphere. It was aimed to develop an appropriate neural network model in order to predict ozone concentrations in various temporal scales as a function of meteorological variables and air quality parameters. All data were collected from Dilovasi, Turkey as this site represents typical industrial regions with major air pollution problems. In the study performance of the multilayer perceptron models were tested for both annual and seasonal periods as meteorological conditions highly influence the ozone levels. Among the various architectures, a network of two hidden layers with fifteen neurons was found to give successful predictions. Modeling efficiency of the developed network was also evaluated for day light and night time data of warming season exhibiting highest ozone levels. Furthermore, principle component analysis was performed by using annual data in order to reduce the number of input variables describing ozone formation. Model run with principle components has also provided satisfying performance.     

不同设计参数对雨水湿地水量水质的调控规律

基于前置塘+二阶表流湿地组合的雨水湿地系统的室内降雨径流模拟实验数据,研究了不同降雨重现期、不同常水位、不同湿地出水口高度、不同湿地级数以及不同污染负荷等设计参数对湿地水量水质调控效果的影响规律,研究结果表明:前置塘+二阶湿地组合的雨水湿地系统通过截留、缓冲和存储作用,对不同降雨径流条件下的产流时间、流量、径流削减率具有多重调控作用,延长了污染物在流域内部的滞留时间,减少了污染负荷的输出,对降雨径流过程中污染物总量具有较好的截留效果。并随设计参数的变化有明显的变化规律。随着降雨重现期的增加,湿地出水口高度的降低,湿地常水位的增加,以及湿地级数的减少,湿地出流量增加,产流时间提前,出流持续时间延长,径流削减率降低。从场次降雨污染物平均浓度(EMC)削减率上看,降雨过程中,雨水湿地仅对SS削减比较明显,削减率达70%—80%,对其他污染物浓度的削减效果不明显。从场次降雨污染物总量削减率来看,雨水湿地对降雨径流污染物具有较好的截留效果,并随着降雨重现期减少、湿地出水口高度增加、湿地常水位降低,呈逐渐增加趋势。     

Effect of Precipitation Variability on Pollutant Concentrations in Soil: Implications for Exposure and Risk Assessments

Concentrations of toxic pollutants in surface soils must be predicted in order to assess exposures and risks that may arise from emissions at incinerators and other air pollution sources. At present, concentrations are predicted using deterministic models and time-averaged values of input parameters. This steady-state equilibrium approach does not address variability in the underlying transport and fate processes. This paper explores the variability of pollutant concentrations in surface soils that arises from precipitation, an intermittent process that governs wet deposition and leaching processes. Using long-term (45 to 50 years) historical records at 6 climato-logically diverse sites, concentrations predicted using the steady-state approach are compared to those predicted using a dynamic numerical model that simulates dry and wet deposition, leaching, and pollutant accumulation in the surface layer of soil using a daily time step. The models are compared for pollutants of low, medium, and high water solubility. Both models show that predictions depend strongly on the pollutant solubility and the precipitation pattern at the location. Average concentrations differed between locations by a factor of up to 4 due to precipitation patterns; the solubility of the pollutant had a much more pronounced effect. Both models produced similar long-term trends, for example, the duration of the period needed to achieve a quasi-steady-state pollutant concentration. However, for soluble pollutants, the dynamic model produced maximum 24-hr average concentrations that exceeded long-term averages by 4 to 8 times, and long-term predictions of the dynamic model exceeded predictions of the steady-state model by 1.9 to 3.6 times (depending on the site). These differences are caused by the steady-state assumption that deposition and leaching occur continuously. While the steady-state model can be used to estimate long-term trends of moderately to highly insoluble pollutants, the dynamic model should be used to predict short-term, maximum concentrations and both short- and long-term averages of soluble pollutants. Site-specific exposure and risk assessments should consider temporal variation and the use of a dynamic model if concentrations of soluble pollutants approach risk-based target levels.     

An open-air system for exposing forest-canopy branches to ozone pollution

We developed a chamberless system to expose branches to elevated concentrations of ozone with little alteration of micro-meteorological conditions. In a 35-year-old stand of sugar maple (Acer saccharum Marsh.), scaffolding and a platform (14 m in height) provided access to 10 branches and ten paired controls within the canopy. Ozone was delivered to the canopy through a manifold and an array of loops (38 cm in diameter) of teflon tubing individually fitted to each branch. Ozone-enriched air was discharged through numerous small holes in each loop positioned beneath the exposed foliage. A sampling system controlled by a microcomputer monitored ozone concentrations for each loop by means of composite air samples from 12 leaves, drawn through small teflon tubes (1.65 mm diameter) attached to the petioles. On average, coefficients of variation for ozone concentrations for the sample points within each branch loop were less than 50%. Between 0900 and 1700 h for 68 d of exposure, the mean hourly ozone concentrations among the branches averaged 95nmol mol⁻¹ (±13SD), about twice the ambient mean. Frequency distributions of mean hourly concentrations during exposure were unimodal and approximately log-normal, comparable to ambient ozone concentrations. The open-air loop system enables exposure of branches to gaseous pollutants under relatively natural conditions.     

Ozone, air pollution, and respiratory health.

Of the outdoor air pollutants regulated by the Clean Air Act of 1970 (and recently revised in 1990), ozone has been the one pollutant most difficult to control within the federal standards. The known human health effects are all on the respiratory system. At concentrations of ozone which occur during summer air-pollution episodes in many urban metropolitan areas of the United States, a portion of the healthy population is likely to experience symptoms and reversible effects on lung function, particularly if exercising heavily outdoors. More prolonged increase in airway responsiveness and the presence of inflammatory cells and mediators in the airway lining fluid may also result from these naturally occurring exposures. Serial exposures to peak levels of ozone on several consecutive days are more characteristic of pollution episodes in the Northeast United States and may be associated with recurrent symptoms. No "high-risk" or more sensitive group has been found, in contrast to the case of sulfur dioxide, to which asthmatics are more susceptible than normals. The occurrence of multiple exposure episodes within a single year over many years in some areas of California has led to studies looking for chronic effects of ozone exposure on the lung. To date, no conclusive studies have been reported, although further work is under way. Much of what we know about the effects of this gas on the lung are based on controlled exposures to pure gas within an environmental exposure laboratory. Interactions between substances which commonly co-occur in air-pollution episodes are also under investigation.     

Effects of Air Pollution and the Introduction of the London Low Emission Zone on the Prevalence of Respiratory and Allergic Symptoms in Schoolchildren in East London: A Sequential Cross-Sectional Study

The adverse effects of traffic-related air pollution on children’s respiratory health have been widely reported, but few studies have evaluated the impact of traffic-control policies designed to reduce urban air pollution. We assessed associations between traffic-related air pollutants and respiratory/allergic symptoms amongst 8–9 year-old schoolchildren living within the London Low Emission Zone (LEZ). Information on respiratory/allergic symptoms was obtained using a parent-completed questionnaire and linked to modelled annual air pollutant concentrations based on the residential address of each child, using a multivariable mixed effects logistic regression analysis. Exposure to traffic-related air pollutants was associated with current rhinitis: NOx (OR 1.01, 95% CI 1.00–1.02), NO₂ (1.03, 1.00–1.06), PM₁₀ (1.16, 1.04–1.28) and PM_2.5 (1.38, 1.08–1.78), all per μg/m³ of pollutant, but not with other respiratory/allergic symptoms. The LEZ did not reduce ambient air pollution levels, or affect the prevalence of respiratory/allergic symptoms over the period studied. These data confirm the previous association between traffic-related air pollutant exposures and symptoms of current rhinitis. Importantly, the London LEZ has not significantly improved air quality within the city, or the respiratory health of the resident population in its first three years of operation. This highlights the need for more robust measures to reduce traffic emissions.