A temporal, multicity model to estimate the effects of short-term exposure to ambient air pollution on health

Background

Countries worldwide are expending significant resources to improve air quality partly to improve the health of their citizens. Are these societal expenditures improving public health?

Objectives

We consider these issues by tracking the risk of death associated with outdoor air pollution over both space and time in Canadian cities.

Materials and methods

We propose two multi-year estimators that use current plus several previous years of data to estimate current year risk. The estimators are derived from sequential time series analyses using moving time windows. To evaluate the statistical properties of the proposed methods, a simulation study with three scenarios of changing risk was conducted based on 12 Canadian cities from 1981 to 2000. Then an optimal estimator was applied to 24 of Canada’s largest cities over the 17-year period from 1984 to 2000.

Results

The annual average daily concentrations of ozone appeared to be increasing over the time period, whereas those of nitrogen dioxide were decreasing. However, the proposed method returns different time trends in public health risks. Evidence for some monotonic increasing trends in the annual risks is weak for O₃ (p = 0.3870) but somewhat stronger for NO₂ (p = 0.1082). In particular, an increasing time trend becomes apparent when excluding year 1998, which reveals lower risk than proximal years, even though concentrations of NO₂ were decreasing. The simulation results validate our two proposed methods, producing estimates close to the preassigned values.

Conclusions

Despite decreasing ambient concentrations, public health risks related to NO₂ appear to be increasing. Further investigations are necessary to understand why the concentrations and adverse effects of NO₂ show opposite time trends.     

银川市大气主要污染物特征与健康风险评价

目的 为了解2020年银川三区两县一市环境大气污染特征,评价其大气质量及大气污染物对人群健康的影响.方法 基于2020年银川各区县大气污染情况,采用美国环境保护署(USEPA)推荐的健康风险模型估算各地大气中SO2、NO2、PM10、PM2.5人群健康风险.结果 2020年银川各区县PM10年均浓度、PM2.5年均浓度...     

PM2.5 and ozone health impacts and disparities in New York City: sensitivity to spatial and temporal resolution

Air quality health impact assessment (HIA) synthesizes information about air pollution exposures, health effects, and population vulnerability for regulatory decision-making and public engagement. HIAs often use annual average county or regional data to estimate health outcome incidence rates that vary substantially by season and at the subcounty level. Using New York City as an example, we assessed the sensitivity of estimated citywide morbidity and mortality attributable to ambient fine particulate matter (PM_2.5) and ozone to the geographic (county vs. neighborhood) and temporal (seasonal vs. annual average) resolution of health incidence data. We also used the neighborhood-level analysis to assess variation in estimated air pollution impacts by neighborhood poverty concentration. Estimated citywide health impacts attributable to PM_2.5 and ozone were relatively insensitive to the geographic resolution of health incidence data. However, the neighborhood-level analysis demonstrated increasing impacts with greater neighborhood poverty levels, particularly for PM_2.5-attributable asthma emergency department visits, which were 4.5 times greater in high compared to low-poverty neighborhoods. PM_2.5-attributable health impacts were similar using seasonal and annual average incidence rates. Citywide ozone-attributable asthma morbidity was estimated to be 15 % lower when calculated from seasonal, compared to annual average incidence rates, as asthma morbidity rates are lower during the summer ozone season than the annual average rate. Within the ozone season, 57 % of estimated ozone-attributable emergency department for asthma in children occurred in the April–June period when average baseline incidence rates are higher than in the July–September period when ozone concentrations are higher. These analyses underscore the importance of utilizing spatially and temporally resolved data in local air quality impact assessments to characterize the overall city burden and identify areas of high vulnerability.     

应用伤残调整寿命年评价我国城市大气颗粒物污染的人群健康效应

目的 评价大气颗粒物污染引起我国城市居民伤残调整寿命年(disability adjusted life years,DALYs)的损失.方法 以2006年我国656个城市的城市人口作为暴露人口,以国家控制大气质量监测体系中各城市的可吸入颗粒物(particulate matter with an aerodynamic diameter less than 10 microns,PM_(10))年均浓度为暴露水平,应用DALYs指标,评价我国城市大气颗粒物污染的人群健康效应.结果 2006年大气颗粒物污染能引起我国城市居民(50.66±9.52)万例早逝,(15.66±4.12)万例慢性支气管炎患者,(1264.05±522.97)万例内科门诊患者,(9.99±5.04)万例心血管疾病住院患者和(7.20±0.82)万例呼吸系统疾病住院患者.2006年归因于城市大气颗粒物污染的DALYs损失总计为(526.22±99.43)万人年,其中由早逝引起的百分率为96.26%(506.55/526.22).城市颗粒物污染越重,城市人口越多,则相应的DALYs损失越大.结论 大气颗粒物污染已对我国城市居民的健康造成了较大的影响,从公共卫生的角度说明了加强治理大气污染的必要性和迫切性.     

Effects of particulate air pollution on systolic blood pressure: A population-based approach

Given the hypothesis that particulate air pollution is associated with systolic blood pressure, the effect of daily concentrations of air pollution on blood pressure was assessed in 2612 elderly subjects in the urban area of Bordeaux, France. Blood pressure was measured by a digital monitor. Particle concentrations (PM10) were obtained from the AIRAQ association that operates a local monitoring network of the air quality. To represent the ambient urban air pollution, stations had to be sufficiently correlated (i.e., correlation >0.70) and to have sufficiently similar mean levels of pollution. Linear regression was used to model the association between concentrations of particles (PM10) and systolic blood pressure. We observed associations between the fifth lag hour and systolic blood pressure for an increase of 10 microg/m3 of PM10 (beta = -1.12, 95% confidence interval: [-1.90; -0.30]). Despite contradictory results, fine particles must be considered nowadays as a major component of atmospheric air pollution in which everything must be put into practice in terms of public health actions in order to protect the general population and particularly the elderly group.     

Environmental risks to public health in the United Arab Emirates: a quantitative assessment and strategic plan

Background: Environmental risks to health in the United Arab Emirates (UAE) have shifted rapidly from infectious to noninfectious diseases as the nation has developed at an unprecedented rate. In response to public concerns over newly emerging environmental risks, the Environment Agency–Abu Dhabi commissioned a multidisciplinary environmental health strategic planning project.Objectives: In order to develop the environmental health strategic plan, we sought to quantify the illnesses and premature deaths in the UAE attributable to 14 environmental pollutant categories, prioritize these 14 risk factors, and identify interventions.Methods: We estimated the disease burden imposed by each risk factor using an attributable fraction approach, and we prioritized the risks using an empirically tested stakeholder engagement process. We then engaged government personnel, scientists, and other stakeholders to identify interventions.Results: The UAE’s environmental disease burden is low by global standards. Ambient air pollution is the leading contributor to premature mortality [~ 650 annual deaths; 95% confidence interval (CI): 140, 1,400]. Risk factors leading to > 10,000 annual health care facility visits included occupational exposures, indoor air pollution, drinking water contamination, seafood contamination, and ambient air pollution. Among the 14 risks considered, on average, outdoor air pollution was ranked by the stakeholders as the highest priority (mean rank, 1.4; interquartile range, 1–2) and indoor air pollution as the second-highest priority (mean rank 3.3; interquartile range, 2–4). The resulting strategic plan identified 216 potential interventions for reducing environmental risks to health.Conclusions: The strategic planning exercise described here provides a framework for systematically deciding how to invest public funds to maximize expected returns in environmental health, where returns are measured in terms of reductions in a population’s environmental burden of disease.     

The role of particulate size and chemistry in the association between summertime ambient air pollution and hospitalization for cardiorespiratory diseases.

In order to address the role that the ambient air pollution mix, comprised of gaseous pollutants and various physical and chemical measures of particulate matter, plays in exacerbating cardiorespiratory disease, daily measures of fine and coarse particulate mass, aerosol chemistry (sulfates and acidity), and gaseous pollution (ozone, nitrogen dioxide, sulfur dioxide, and carbon monoxide) were collected in Toronto, Ontario, Canada, in the summers of 1992, 1993, and 1994. These time series were then compared with concurrent data on the number of daily admissions to hospitals for either cardiac diseases (ischemic heart disease, heart failure, and dysthymias) or respiratory diseases (tracheobronchitis, chronic obstructive long disease, asthma, and pneumonia). After adjusting the admission time series for long-term temporal trends, seasonal variations, the effects of short-term epidemics, day of the week effects, and ambient temperature and dew point temperature, positive associations were observed for all ambient air pollutants for both respiratory and cardiac diseases. Ozone was least sensitive to adjustment for the gaseous and particulate pollution measures. However, the association between the health outcomes and carbon monoxide, fine and coarse mass, sulfate levels and aerosol acidity could be explained by adjustment for exposure to gaseous pollutants. Increases in ozone, nitrogen dioxide, and sulfur dioxide equivalent to their interquartile ranges corresponded to an 11% and 13% increase in daily hospitalizations for respiratory and cardiac diseases, respectively. The inclusion of any one of the particulate air pollutants in multiple regression models did not increase these percentages. Particle mass and chemistry could not be identified as an independent risk factor for the exacerbation of cardiorespiratory diseases in this study beyond that attributable to climate and gaseous air pollution. We recommend that effects of particulate matter on health be assessed in conjunction with temporally covarying gaseous air pollutants.     

Long-term trends in ambient particulate matter,chemical composition,and associated health risk and mortality burden in Hong Kong (1995–2016)

Hong Kong is one of the special administrative regions in China and a densely populated city with poor air quality. The impact of high pollutant concentrations, especially ambient particulate matter (PM), on human health is of major concern. This study reported the temporal trends of PM masses and chemical components and assessed the PM pollution-related health risk and mortality burden in Hong Kong over a 22-year period (1995–2016). The results showed that the ambient PM increased before 2005 and then decreased gradually with overall downward trends of ??0.61 μg m^?3 year^?1 for inhalable PM (PM₁₀) and ??1.30 μg m^?3 year^?1 for fine PM (PM_2.5). No statistically significant changes were observed for secondary inorganic components (SO₄^2?, NO₃^?, and NH₄⁺), while significant decreasing trends were found for total carbon (TC) and other water-soluble irons (Na⁺, Cl^?, and K⁺). The long-term variabilities of the trace elements differed greatly with species. A health risk assessment revealed that the annual inhalational carcinogenic risk from As, Cd, Ni, Cr, and Pb was always lower than the accepted criterion of 10^?6, whereas the total noncarcinogenic risk from As, Cd, Ni, Cr, and Mn frequently exceeded the safe level of 1. Further, a health burden assessment indicated that the annual mean number of premature mortalities attributable to PM_2.5 exposure was 2918 (95% CI: 1288, 4279) cases during the period of 2001–2016. Both health risk and mortality burden presented constant reductions in recent years, confirming the health benefits of air pollution control measures and the importance of further mitigation efforts.     

A class of non-linear exposure-response models suitable for health impact assessment applicable to large cohort studies of ambient air pollution

The effectiveness of regulatory actions designed to improve air quality is often assessed by predicting changes in public health resulting from their implementation. Risk of premature mortality from long-term exposure to ambient air pollution is the single most important contributor to such assessments and is estimated from observational studies generally assuming a log-linear, no-threshold association between ambient concentrations and death. There has been only limited assessment of this assumption in part because of a lack of methods to estimate the shape of the exposure-response function in very large study populations. In this paper, we propose a new class of variable coefficient risk functions capable of capturing a variety of potentially non-linear associations which are suitable for health impact assessment. We construct the class by defining transformations of concentration as the product of either a linear or log-linear function of concentration multiplied by a logistic weighting function. These risk functions can be estimated using hazard regression survival models with currently available computer software and can accommodate large population-based cohorts which are increasingly being used for this purpose. We illustrate our modeling approach with two large cohort studies of long-term concentrations of ambient air pollution and mortality: the American Cancer Society Cancer Prevention Study II (CPS II) cohort and the Canadian Census Health and Environment Cohort (CanCHEC). We then estimate the number of deaths attributable to changes in fine particulate matter concentrations over the 2000 to 2010 time period in both Canada and the USA using both linear and non-linear hazard function models.     

Daily visibility and mortality: Assessment of health benefits from improved visibility in Hong Kong

Visibility in Hong Kong has deteriorated significantly over 40 years with visibility below 8 km in the absence of fog, mist, or precipitation, increasing from 6.6 days in 1968 to 54.1 days in 2007. We assessed the short-term mortality effects of daily loss of visibility. During 1996-2006, we obtained mortality data for non-accidental and cardiorespiratory causes, visibility recorded as visual range in kilometers, temperature, and relative humidity from an urban observatory, and concentrations of four criteria pollutants. A generalized additive Poisson regression model with penalized cubic regression splines was fitted to control for time variant covariates. For non-accidental mortality, an interquartile range (IQR) of 6.5 km decrease in visibility at lag 0-1 days was associated with an excess risk (ER%) [95% CI] of 1.13 [0.49, 1.76] for all ages and 1.37 [0.65, 2.09] for ages 65 years and over; for cardiovascular mortality of 1.31 [0.13, 2.49] for all ages, and 1.72 [0.44, 3.00] for ages 65 years and over; and for respiratory mortality of 1.92 [0.49, 3.35] for all ages and 1.76 [0.28, 3.25] for ages 65 years and over. The estimated ER% for daily mortality derived from both visibility and air pollutant data were comparable in terms of magnitude, lag pattern, and exposure-response relationships especially when using particulate matter with aerodynamic diameter ≤10 μm to predict the mortality associated with visibility. Visibility provides a useful proxy for the assessment of environmental health risks from ambient air pollutants and a valid approach for the assessment of the public health impacts of air pollution and the benefits of air quality improvement measures in developing countries where pollutant monitoring data are scarce.     

Spatiotemporal pattern of air quality index and its associated factors in 31 Chinese provincial capital cities

Understanding the spatiotemporal characteristics of ambient air quality and identifying the associated factors are helpful to develop integrated interventions to prevent and control air pollution. Based on daily data of air quality index (AQI) in 31 Chinese provincial capital cities in 2014, this study aimed to investigate the spatiotemporal variations of ambient air pollution and the influencing factors. The spatial and temporal patterns of AQI were presented using GIS map and heat map, respectively. We constructed a hierarchical linear model to quantify the effects of meteorological and socioeconomic factors on AQI. In 2014, the air quality nonattainment (AQI >100) rate was 34.6% on average (1.9 to 74.4%). Air pollution levels were highest in winters and lowest in summers. We found substantial spatial variations of AQI, with the highest values in the middle-east area of the North China Plain. The city-level AQI was positively associated with vehicle population, industrial dust emission, and GDP per capital, which cumulatively explained 67.5% of spatial variations of AQI. The city-level AQI also increased with city’s annual atmospheric pressure but decreased with annual mean temperature. Daily AQI within a city decreased with daily temperature, sunshine duration, wind speed, precipitation, and relative humidity. The national analyses indicate that the ambient air quality in China exhibits significant geographical and seasonal variations which were mainly driven by socioeconomic and meteorological factors. The findings would help to understand the underlying reasons for spatial health disparities and would provide important information to guide targeted policy response to ambient air pollution.     

Airborne trace metals from coal combustion in Beijing

Prior studies have measured elevated ambient concentrations of hazardous metals in Beijing, attributable to coal combustion. The 2008 Olympic Games led to an intense investment in air pollution controls at the major power plants in the region, accounting for 30% of coal combustion in Beijing. Recently Chinese coal beds have been characterized in the World Coal Quality Index, facilitating the development of trace metal emission factors for Beijing coals. This study quantifies the relative value of the power plant air pollution controls in terms of public health risk from chronic exposure to trace metals. Ambient concentrations from power plants were estimated using an atmospheric dispersion model (CALPUFF), outlining spatial and temporal variations. The following toxic, refractory metals were evaluated for health risk using the USEPA Integrated Risk Information System: antimony, arsenic, beryllium, cadmium, chromium, cobalt, copper, lead, manganese, nickel, and selenium. Stringent use of power plant air pollution controls significantly reduces population risk, averting a cancer risk of 1 in 5,000. However, other sources of coal combustion, such as industrial and household uses, are more relevant to public health than power plant emissions. Coal washing has potential to reduce the hazard from these diffuse sources and avert a greater number of potential cancer cases.     

Assessing personal exposure to traffic-related air pollution using individual travel-activity diary data and an on-road source air dispersion model

Assessing personal exposure to traffic-related air pollution poses challenges due to the limited availability of human movement data and the complexity of modeling air pollution attributable to traffic. This study develops a method for reconstructing individuals’ movement trajectories from travel-activity diaries and assesses exposure by integrating the trajectories with PM_2.5 concentrations that are derived from on-road source air dispersion modeling. It finds that everyone has a unique exposure profile due to a unique combination of movement patterns and concentrations and that being in transit contributes 7.8% of the daily exposure although the amount of time spent in transit is minimal.     

上海市大气污染与居民每日死亡关系的病例交叉研究

目的 以病例交叉的研究方法，估计大气污染急性暴露对上海市居民每日死亡的影响，并探讨该设计用于大气污染急性健康效应研究的可行性。方法 采用病例交叉设计的方法分析上海市2000年6月1日至2001年12月31日大气污染与居民每日总死亡和分疾病别死亡的关系，同时比较双向对照设计和单向回顾性对照设计研究结果的差异。结果 采用不同的对照选择方案，病例交叉设计的研究结果变化较大；采用双向1：6的对照设计，大气可吸入颗粒物(PMl0)、二氧化硫(SO2)、二氧化氮(NO2)48h平均浓度每增加10μg／m^3，上海市城区居民总死亡发生的相对危险度分别为1．003(95％CI：1．001～1．005)、1．016(95％CI：1．011～1．021)、1．020(95％CI：1．012～1．027)。结论 上海市城区目前的PMl0、SO2、NO2水平对居民死亡确有影响；病例交叉设计是一种研究大气污染急性健康效应的有效工具。     

Evaluation of the agreement between modeled and monitored ambient hazardous air pollutants in California

Elevated breast cancer incidence rates in urban areas have led to speculation regarding the potential role of air pollution. In order to inform the exposure assessment for a subsequent breast cancer study, we evaluated agreement between modeled and monitored hazardous air pollutants (HAPs). Modeled annual ambient concentrations of HAPs in California came from the US Environmental Protection Agency’s National Air Toxics Assessment database for 1996, 1999, 2002, and 2005 and corresponding monitored data from the California Air Resources Board’s air quality monitoring program. We selected 12 compounds of interest for our study and focused on evaluating agreement between modeled and monitored data, and of temporal trends. Modeled data generally underestimated the monitored data, especially in 1996. For most compounds agreement between modeled and monitored concentrations improved over time. We concluded that 2002 and 2005 modeled data agree best with monitored data and are the most appropriate years for direct use in our subsequent epidemiologic analysis.     

Ambient air pollution and apnea and bradycardia in high-risk infants on home monitors

Background: Evidence suggests that increased ambient air pollution concentrations are associated with health effects, although relatively few studies have specifically examined infants.Objective: We examined associations of daily ambient air pollution concentrations with central apnea (prolonged pauses in breathing) and bradycardia (low heart rate) events among infants prescribed home cardiorespiratory monitors.Methods: The home monitors record the electrocardiogram, heart rate, and respiratory effort for detected apnea and bradycardia events in high-risk infants [primarily premature and low birth weight (LBW) infants]. From August 1998 through December 2002, 4,277 infants had 8,960 apnea event-days and 29,450 bradycardia event-days in > 179,000 days of follow-up. We assessed the occurrence of apnea and bradycardia events in relation to speciated particulate matter and gaseous air pollution levels using a 2-day average of air pollution (same day and previous day), adjusting for temporal trends, temperature, and infant age.Results: We observed associations between bradycardia and 8-hr maximum ozone [odds ratio (OR) = 1.049 per 25-ppb increase; 95% confidence interval (CI), 1.021–1.078] and 1-hr maximum nitrogen dioxide (OR =1.025 per 20-ppb increase; 95% CI, 1.000–1.050). The association with ozone was robust to different methods of control for time trend and specified correlation structure. In secondary analyses, associations of apnea and bradycardia with pollution were generally stronger in infants who were full term and of normal birth weight than in infants who were both premature and LBW.Conclusions: These results suggest that higher air pollution concentrations may increase the occurrence of apnea and bradycardia in high-risk infants.     

Double burden of deprivation and high concentrations of ambient air pollution at the neighbourhood scale in Montreal, Canada

Some neighbourhoods in urban areas are characterised by concentrations of socially and materially deprived populations. Additionally, levels of ambient air pollution in a city can be variable at the local scale and can create disparities in air quality between neighbourhoods. Socioeconomic and physical characteristics of neighbourhood environments can affect the health and well-being of local residents. In this paper we identify whether neighbourhoods in Montreal, Canada characterised by social and material deprivation have higher levels of ambient air pollution than do others.We collected two-week integrated samples of nitrogen dioxide (NO₂) at 133 sites in Montreal during three seasons between 2005 and 2006. We used these data in a geographic information system, along with data describing characteristics of land use, roads, and traffic, to create a spatial model of predicted mean annual concentrations of NO₂ across Montreal. Next, we collected neighbourhood socioeconomic information for 501 census tracts and overlaid their boundaries on the pollution surface. We calculated Pearson correlation coefficients and 95% confidence intervals (CI) between neighbourhood-level indicators of deprivation and levels of ambient NO₂.We found associations between concentrations of NO₂ and neighbourhood-level indicators of material deprivation, including median household income, and with indicators of social deprivation, including proportion of people living alone. We identified specific neighbourhoods that were characterised by a double burden of high levels of deprivation and high concentrations of ambient NO₂. Because of the particular social geography in Montreal, we found that not all deprived neighbourhoods had high levels of pollution and that some affluent neighbourhoods in the downtown core had high levels. Our results underscore the importance of considering social contexts in interpreting general associations between social and environmental risks to population health.     

Air pollution,avoidance behaviour and children's respiratory health: Evidence from England

Despite progress in air pollution control, concerns remain over the health impact of poor air quality. Governments increasingly issue air quality information to enable vulnerable groups to avoid exposure. Avoidance behaviour potentially biases estimates of the health effects of air pollutants. But avoidance behaviour imposes a cost on individuals and therefore may not be taken in all circumstances. This paper exploits panel data at the English local authority level to estimate the relationship between children's daily hospital emergency admissions for respiratory diseases and common air pollutants, while allowing for avoidance behaviour in response to air pollution warnings. A 1% increase in nitrogen dioxide or ozone concentrations increases hospital admissions by 0.1%. For the subset of asthma admissions – where avoidance is less costly – there is evidence of avoidance behaviour. Ignoring avoidance behaviour, however, does not result in statistically significant underestimation of the health effect of air pollution.     

Health effects costs of particulate air pollution.

We conducted a cross-sectional study in December 1994 in three metropolitan areas of the Rhone-Alpes region in France (Lyon, Grenoble, and Chambéry; total number of inhabitants = 970,000) to assess the medical costs resulting from exposure to particulate air pollution. Probability samples of the general population (508 families, 1265 subjects) and of the physicians (395) and 13 hospital respiratory care and emergency units in the study area provided data on the prevalence of respiratory disorders and on medical care usage. Measurements from air-quality monitoring networks were used to ascribe a fraction of the respiratory morbidity to the ambient air particle concentrations present during the study period, on the basis of attributable risk estimates drawn from recent meta-analyses. The medical care usage and absenteeism related to respiratory disorders were converted into direct and indirect medical and social costs by use of a "cost of illness" approach. These costs were extrapolated to annual costs of disease attributable to particulate pollution in 1994, using daily values of air pollution. The average particulate concentrations during the study period were moderate (39, 41, and 10 micrograms/m3 in the three cities), yielding attributable fractions that ranged between 0.6% and 13.8% according to the health condition and to the city. Three hundred ninety-five subjects reported respiratory symptoms (prevalence, 31.2%) during the study period; 1182 patients visited a doctor and 158 used hospital services. The extrapolated annual estimates of the attributable cost of respiratory diseases for a population of 1 million range between 79 and 135 million French francs (FF) (20th and 80th percentiles of the cost distribution, after a Monte Carlo simulation, respectively; 50th percentile, 107 x 10(6) FF [16.3 x 10(6) Euros]). Over-the counter drug consumption represents the largest cost item (approximately 44% of total costs), followed by wage losses (38%). Hospital expenditures amount to a low percentage of total costs (about 5%) because most respiratory disorders do not require hospital care. Mortality was not considered in this study. Most of these costs occur at relatively low levels of air pollution (67% of the total annual costs are incurred during days with particle concentrations lower than 50 micrograms/m3). Such substantial figures are useful for assessing the social impacts of air pollution and for evaluating the cost efficiency of abatement policies.     

Air pollution and population health: a global challenge

“Air pollution and population health” is one of the most important environmental and public health issues. Economic development, urbanization, energy consumption, transportation/motorization, and rapid population growth are major driving forces of air pollution in large cities, especially in megacities. Air pollution levels in developed countries have been decreasing dramatically in recent decades. However, in developing countries and in countries in transition, air pollution levels are still at relatively high levels, though the levels have been gradually decreasing or have remained stable during rapid economic development. In recent years, several hundred epidemiological studies have emerged showing adverse health effects associated with short-term and long-term exposure to air pollutants. Time-series studies conducted in Asian cities also showed similar health effects on mortality associated with exposure to particulate matter (PM), sulfur dioxide (SO₂), nitrogen dioxide (NO₂) and ozone (O₃) to those explored in Europe and North America. The World Health Organization (WHO) published the “WHO Air Quality Guidelines (AQGs), Global Update” in 2006. These updated AQGs provide much stricter guidelines for PM, NO₂, SO₂ and O₃. Considering that current air pollution levels are much higher than the WHO-recommended AQGs, interim targets for these four air pollutants are also recommended for member states, especially for developing countries in setting their country-specific air quality standards. In conclusion, ambient air pollution is a health hazard. It is more important in Asian developing countries within the context of pollution level and population density. Improving air quality has substantial, measurable and important public health benefits.