清除空气毒物 Taking Toxics out of the Air

美国环境保护署 Environment Protection Agency (epa)

Air toxics are those air pollutants that are known or suspected to cause cancer or other serious health problems such as toxicity in mutagen, reproduction, or biologically and environmentally harmful and accumulating. Each year, millions of tons of air toxics are released into the air, mostly from manmade sources, especially invisible FUGITIVE Emissions. This document describes what air toxics are, where they come from, and how they can impact people and the environment. It also describes the steps being taken by the U.S. Environmental Protection Agency to reduce emissions of air toxics from major industrial sources such as chemical manufacturing plants, petroleum refineries, and steel manufacturing plants.

空气毒物亦即那些已知或可疑诱发癌症或其它严重健康问题，比如生殖毒性、发育毒性，甚或属于环境激素、生物毒物、环境累积毒物等的空气污染物。每年，成百上千万吨空气毒物释放到空气中，主要来自人为污染源，尤其是隐形的“无组织排放”。本文介绍空气毒物是什么，来自哪里，如何影响人和环境。同时也介绍美国环境保护署所采取的措施，用以减少来自主要工业污染源，如化工厂、炼化厂、钢铁厂等的空气毒物排放。

 

The air we breathe can be contaminated with pollutants from factories, vehicles, power plants, and many other sources. These pollutants have long been a major concern because of the harmful effects they sometimes have on people’s health and the environment. Their impact depends on many factors, including the quantity of air pollution to which people are exposed, the duration of the exposures, and the potency of the pollutants. The effects of air pollutants can be minor and reversible (such as eye irritation) or debilitating (such as aggravation of asthma) and even fatal (such as cancer).

我们呼吸的空气，会受到来自工厂、车辆、电厂和其它污染源的污染物的玷污。这些污染物长久以来一直引人深忧，因为它们通常对人们的健康以及我们的环境具有危害影响。其影响基于若干因素，包括人们接触空气污染的程度、时长，以及污染物的毒性。空气污染物的影响可以是轻微且可逆的(比如眼睛感到刺激)，但也可能缠磨日久(比如持续加重的哮喘)，甚或是致命的(比如癌症)。

 

Since 1970, the Clean Air Act has provided the primary framework for protecting people and the environment from the harmful effects of air pollution. A key component of the Clean Air Act is a requirement that the U.S. Environmental Protection Agency (EPA) significantly reduce daily, so-called “routine” emissions of the most potent air pollutants: those that are known or suspected to cause serious health problems such as cancer or birth defects. The Clean Air Act refers to these pollutants as “hazardous air pollutants,” (HAP) but they are also commonly known as toxic air pollutants or, simply, air toxics.

1970年以来，清洁空气法已经为保护人和环境免于空气污染之害建立了初步框架。清洁空气法的一个基本要素是要求美国环境保护署显著减低最有害的空气污染物的日常的排放，即所谓“例行”排放：包括那些已知或可疑诱发严重健康问题，比如癌症或先天缺陷的污染物。清洁空气法确认此类污染物为“有害空气污染物”(HAP)，即一般所指有毒空气污染物，或简单讲，空气毒物。

 

 

WHAT ARE TOXIC AIR POLLUTANTS?

The 1990 Clean Air Act Amendments list 188 toxic air pollutants that EPA is required to control. Examples of toxic air pollutants include benzene, which is found in gasoline; perchloroethylene, which is emitted from some dry cleaning facilities; and methylene chloride, which is used as a solvent and paint stripper by a number of industries. Examples of other listed air toxics include dioxin, asbestos, toluene, and metals such as cadmium, mercury, chromium, and lead compounds.

什么是空气毒物
1990年清洁空气法修正案列出了188种有毒空气污染物，要求EPA加以控制。有毒空气污染物包括苯，日常可见于汽油；四氯乙烯，常由干洗行业排放；以及二氯甲烷，常被用作溶剂或除漆剂，用于若干行业。其它列名的空气毒物包括，二恶英、石棉、甲苯，以及金属，如镉、汞、铬、铅及化合物等。

空气毒物常见的有害性既有急性的(Acute)，更多的是慢性的(Chronic)，包括，但不仅限于，致癌性(Carcinogen)、致突变性(Mutagen)、生殖毒性(Reproduction)、发育毒性(Development)、神经毒性(Neurology)、生物毒性(Biology)；并且还可构成生物积累毒性、环境积累毒性、环境激素、光化学反应、温室效应、臭氧层破坏等多种环境损害。

 

 

WHERE DO AIR TOXICS COME FROM?

Scientists estimate that millions of tons of toxic pollutants are released into the air each year. Most air toxics originate from manmade sources, including both mobile sources (e.g., cars, buses, trucks) and stationary sources (e.g., factories, refineries, power plants). However, some are released in major amounts from natural sources such as forest fires. This document focuses on EPA’s efforts, as of August 2000, to reduce routine (as opposed to accidental) emissions of toxic air pollutants from stationary sources. Routine emissions from stationary sources constitute almost one-half of all manmade air toxics emissions.

空气毒物从哪来的？

科学家们估计每年有成百上千万吨有毒污染物排放到空气中。大部分空气毒物来自人为污染源，包括流动源(如汽车、客车、卡车等)和固定源(如工厂、炼化厂、发电厂等)。也有很大部分来自自然源，比如森林火灾。本文重点讲述，EPA至2000年8月在降低固定源的有害空气污染物的日常排放(相对于偶发排放)方面的工作。

 

There are two types of stationary sources that generate routine emissions of air toxics:
“Major” sources are defined as sources that emit 10 tons per year of any of the listed toxic air pollutants, or 25 tons per year of a mixture of air toxics. Examples include chemical plants, steel mills, oil refineries, and hazardous waste incinerators. These sources may release air toxics from equipment leaks, when materials are transferred from one location to another, or during discharge through emissions stacks or vents. One key public health concern regarding major sources is the health effects on populations located downwind from them.

Fugitive emissions are emissions of gases or vapors from pressurized equipment due to leaks and other unintended or irregular releases of gases, mostly from industrial activities. As well as the economic cost of lost commodities, fugitive emissions contribute to air pollution and climate change. A detailed inventory of greenhouse gas emissions from upstream oil and gas activities in Canada for the year 2000 estimated that fugitive equipment leaks had a global warming potential equivalent to the release of 17 million metric tonnes of carbon dioxide, or 12 per cent of all greenhouse gases emitted by the sector. Venting of natural gas, flaring, accidental releases and storage losses accounted for an additional 38 per cent.

Fugitive emissions present other risks and hazards. Emissions of volatile organic compounds such as benzene from oil refineries and chemical plants pose a long term health risk to workers and local communities. In situations where large amounts of flammable liquids and gases are contained under pressure, leaks also increase the risk of fire and explosion.

Leaks from pressurized process equipment generally occur through valves, pipe connections, mechanical seals, or related equipment. Fugitive emissions also occur at evaporative sources such as waste water treatment ponds and storage tanks. Because of the huge number of potential leak sources at large industrial facilities and the difficulties in detecting and repairing some leaks, fugitive emissions can be a significant proportion of total emissions. Though the quantities of leaked gases may be small, gases that have serious health or environmental impacts can cause a significant problem.

空气毒物日常排放的固定排放源也有两种类型。

“重大”排放源亦即列名空气毒物年排放量超过10吨，或混合空气毒物年排放量超过25吨的。例如化工厂、钢铁厂、炼化厂、以及危险废弃物焚烧厂等。这类排放源排放的空气毒物来源于设备泄漏、物料装卸转运、或排风系统排风管道的泄放。“重大”排放源对公共健康的重要威胁是其对处于下风位置的人群的健康影响。

“重大”固定排放源，产生隐形的“无组织排放”。是气体或蒸气从压力设备中逸漏以及其它无意无规的气体排放，基本都是在生产活动中产生的。无组织排放既有产品损失的经济代价，又是空气污染和气候变化的帮凶。一份针对2000年加拿大油气开采活动温室气体排放的详细清单估算，无序的设备逸漏造成的全球升温指数相当于1700万吨二氧化碳排放量，或占该行业温室气体排放的12%；天然气排风、火炬气、意外泄漏、储罐逸漏则另占38%。

无组织排放还带来其它风险和危害。挥发性有机化合物(VOC)，比如炼化厂、化工厂逸漏的苯，对工人和当地社区造成长期的健康风险。巨量易燃液体、气体压力储存的情况下，微量逸漏也增加了火灾、爆炸风险。

无组织排放首先是在物料转移运输过程中产生。物料装卸、灌装、抽吸等操作不采用密闭措施的，均有大量泄漏排放。其次，物料储存、运输过程中的储罐、槽罐，也是巨大的逸漏排放源；即使罐体及管道、阀门完好无泄漏，槽罐上的排气阀、呼吸阀、安全阀等，为平衡罐内外气压，也会不定时地排放气相物料，大部分就是空气毒物。生产过程中的带压工艺设备的逸漏一般在阀门、管道接头、机械密封、或其它相关设备处产生。也会在蒸发源，如废水处理池、储槽中产生。由于大型工业基地内潜在逸漏点数目巨大，且难以探测和检修，无组织排放可以占到总排放量内很高的比例。尽管各个逸漏点的逸漏量较小，具有严重健康和环境影响的污染气仍会造成显著的问题。
 

“Area” sources consist of smaller sources, each releasing smaller amounts of toxic pollutants into the air. Area sources are defined as sources that emit less than 10 tons per year of a single air toxic, or less than 25 tons per year of a mixture of air toxics. Examples include neighborhood dry cleaners and gas stations. Though emissions from individual area sources are often relatively small, collectively their emissions can be of concern - particularly where large numbers of sources are located in heavily populated areas.

“区域”排放源意指较小的污染排放点，每个只排放较少数量的有毒污染物到空气中。区域排放源定义为年排放量单一空气毒物少于10吨、或混合空气毒物少于25吨的排放点。比如社区中的干洗店、加油站等。尽管单个区域排放源的排放量通常比较小，但其汇集的总量令人担忧 – 尤其是大量此类排放源分布在人口重度密集区的时候。


EPA’s published list of “source categories” now contains 175 categories of industrial and commercial sources that emit one or more toxic air pollutants. For each of these source categories, EPA indicated whether the sources are considered to be “major” sources or “area” sources. The 1990 Clean Air Act Amendments direct EPA to set standards requiring all major sources of air toxics (and some area sources that are of particular concern) to significantly reduce their air toxics emissions.

EPA编印有“排放源类别”，目前包含了175个类别的工业和商业排放源，分别有单个或多种有毒空气污染物排放。对每个类别，EPA列明了其为“重大”排放源或“区域”排放源。1990清洁空气法修正案指示EPA设定标准以要求所有空气毒物重大排放源(以及部分特别令人担忧的区域排放源)显著减少各自的空气毒物排放量。


WHERE DO AIR TOXICS GO?

Once released, toxic pollutants can be carried by the wind, away from their sources, to other locations. Factors such as weather, the terrain (i.e., mountains, plains, valleys), and the chemical and physical properties of a pollutant determine how far it is transported, its concentration at various distances from the source, what kind of physical and chemical changes it undergoes, and whether it will degrade, remain airborne, or deposit to land or water.

空气毒物去哪儿了？

一经散发，有毒污染物可乘风带离其源头，漂往其它地点。天气、地形(山地、平原、山谷等)、污染物本身的物理-化学性质等因素综合作用，共同决定了该污染物传输距离、离源头不同距离上的浓度、其经历的物理-化学变化、是否降解、是否持续留空，抑或飘降土壤或水体。

 

Some pollutants remain airborne and contribute to air pollution problems far from the pollution source. Other pollutants released into the air can be deposited to land and water bodies through precipitation, or by settling directly out of the air onto land or water. Eventually, a large portion of those pollutants deposited near water bodies or small tributaries will reach the water bodies via stormwater runoff or inflow from the tributary streams.

有些污染物持续滞空，并在远离源头处成为空气污染的帮凶。有些散发空中的污染物可以从空气中析出而沉积地面和水体，也可直接沉降。最终，相当部分沉积在水体或其支流附近的污染物会经雨水冲刷或经支流小溪进入水体。

 

Some toxic air pollutants are of particular concern because they degrade very slowly or not at all, as in the case of metals such as mercury or lead. These persistent air toxics (as they are called) can remain in the environment for a long time (or forever, in the case of metals) and can be transported great distances.

有些有毒空气污染物尤其令人担忧，因为它们降解很慢，或干脆不会降解，比如金属中的汞和铅。这类顽固空气毒物(正如其名)可在环境中存在超长时间 (抑或永久，比如金属物)，并能传播超长距离。

 

Often, persistent air toxics reach the ground, evaporate back into the atmosphere, and are then transported further until they are deposited on the ground again. Repeated cycles of transport, deposition, and evaporation can move toxic air pollutants very long distances. For example, toxic pollutants such as toxaphene, a pesticide used primarily in the cotton belt, have been found in the Antarctic, thousands of miles from their likely emissions sources.

经常性地，顽固空气毒物到达地面，再次蒸发进入大气，然后经传播至更远，直至再次沉积地面。反复循环的输运、沉积、蒸发可以使有毒空气污染物传输超长距离。例如，有毒污染物毒杀芬 toxaphene，一种基本用于产棉各州的杀虫剂，在南极也被测到，距离其可能的散发源已有数千英哩之遥。

 

 

HOW ARE PEOPLE EXPOSED TO AIR TOXICS?

People are exposed to toxic air pollutants in many ways that can pose health risks, such as by:

• Breathing contaminated air.

• Eating contaminated food products, such as fish from contaminated waters; meat, milk, or eggs from animals that fed on contaminated plants; and fruits and vegetables grown in contaminated soil on which air toxics have been deposited. 

• Drinking water contaminated by toxic air pollutants. 

• Eating contaminated soil. Young children are especially vulnerable because they may ingest contaminated soil from their hands or from objects they place in their mouths. 

• Touching (skin contact) contaminated soil, dust, or water (for example, during recreational use of contaminated water bodies).

 

人们如何接触到到空气毒物？

人们通过多种途径接触空气毒物，并造成健康风险，比如，

吸入受污染空气

食用受污染食品，比如受污染水体中的鱼；受污染饲料饲养的动物所生产的肉类、乳制品、蛋类；空气毒物沉积土壤生长的水果、蔬菜。
接触(皮肤接触)有污染的土壤、尘埃、或水体等

 

Once toxic air pollutants enter the body, some persistent toxic air pollutants accumulate in body tissues. Also, through a phenomenon called biomagnification, predators typically accumulate even greater pollutant concentrations than their contaminated prey. As a result, people and other animals at the “top” of the food chain who eat contaminated fish or meat are exposed to concentrations that are much higher than the concentrations in the water, air, or soil.

 

Fish consumption advisories have been issued for thousands of water bodies nationwide, including over 52,000 lakes and over 238,000 miles of rivers. As of December 1999, 40 states have consumption advisories about mercury-contaminated fish for specific water bodies. Eleven of those states have issued state-wide advisories for freshwater lakes and rivers. Many of these water bodies were once thought to be relatively pristine. However, EPA is now finding that deposition from the air may be a major source of the pollution in these water bodies.

有毒空气污染物一旦进入人体，有些顽固有毒空气污染物会在人体组织中积累。另外，通过一种称为生物放大效应的现象，掠食者一定会积累比其受污染的猎物多得多的污染物。其结果，人类和其它处于食物链顶端的动物食用受污染的鱼和肉就必然接触到比单纯水、空气或土壤中浓度高得多的污染物。

美国国内已经对成千上万水体印制了鱼类消费建议，覆盖52000处湖泊、238000英哩河流。至1999年12月，40个州提出了针对特定水体汞污染鱼类的消费建议。其中11个州颁布了淡水湖泊河流的消费警告。其中很多水体曾被认为是相当原生态的。然而，EPA目前发现，空气中污染物沉积可能是这些水体污染的重要来源。

 

HEALTH EFFECTS

People who are exposed to toxic air pollutants at sufficient concentrations and for sufficient durations may increase their chances of getting cancer or experiencing other serious health effects. Depending on which air toxics an individual is exposed to, these health effects can include damage to the immune system, as well as neurological, reproductive (e.g., reduced fertility), developmental, and respiratory problems. A growing body of evidence indicates that some air toxics (e.g., DDT, dioxins, and mercury) may disturb hormonal (or endocrine) systems. In some cases this happens by pollutants either mimicking or blocking the action of natural hormones. Health effects associated with endocrine disruption include reduced male fertility, birth defects, and breast cancer.

健康危害

人只要长时间接触一定浓度的有毒空气污染物就会增加其罹患癌症或其它疾害的机会。根据个体接触的空气毒物种类，这些疾害常见有免疫系统损伤、也可见神经系统、生殖系统(生育力下降)、发育或呼吸系统问题。不断增加的证据显示，某些空气毒物(DDT、二恶英、汞等)可干扰荷尔蒙(或内分泌)系统。某些例证中，污染物或者拟代或者阻断了天然荷尔蒙的作用。与内分泌紊乱相关的疾害包括男性生殖力下降、先天残缺、乳腺癌等。

 

HOW DO AIR TOXICS AFFECT THE ENVIRONMENT?

Toxic pollutants in the air, or deposited on soils or surface waters, can have a number of environmental impacts. Like humans, animals can experience health problems if they are exposed to sufficient concentrations of air toxics over time. Numerous studies conclude that deposited air toxics are contributing to birth defects, reproductive failure, and disease in animals. Persistent toxic air pollutants are of particular concern in aquatic ecosystems because the pollutants accumulate in sediments and may biomagnify in tissues of animals at the top of the food chain to concentrations many times higher than in the water or air. Toxic pollutants that mimic hormones also pose a threat to the environment. In some wildlife (e.g., birds, shellfish, fish, and mammals), exposures to pollutants such as DDT, dioxins, and mercury have been associated with decreased fertility, decreased hatching success, damaged reproductive organs, and altered immune systems.
空气毒物如何损害环境？

有毒污染物存在于空气中或沉积到土壤或地表水体可带来一系列环境损害。与人类相似，动物在长时期接触高浓度空气毒物后也会出现健康问题。许多研究都得出结论，沉积的空气毒物也是动物先天残缺、繁殖缺损、以及各种疾病的幕后黑手。顽固性有毒空气污染物对水生态环境的影响尤为令人担忧，此类污染物在水体底泥中累积，并会经生物链放大转移至食物链顶层的动物身体组织中，浓度可比在水体或空气中高许多倍。有些野生动物(比如鸟、甲壳类、鱼类或水生哺乳类)接触诸如DDT、二恶英、汞等污染物，也会导致生育力降低、筑巢成功率降低、生殖系统受损、免疫系统改变等问题。

WHAT HAS EPA DONE TO REDUCE AIR TOXICS?

 

The Pre-1990 “Risk-Only” Approach

Prior to 1990, the Clean Air Act directed EPA to regulate toxic air pollutants based on the risks each pollutant posed to human health. Specifically, the Act directed EPA to: 

•      Identify all pollutants that caused “serious and irreversible illness or death.”

•      Develop standards to reduce emissions of these pollutants to levels that provided an “ample margin of safety” for the public.

 

1990年前“只查风险”方法

1990年以前，清洁空气法案指令EPA根据各个污染物对人的健康风险管控空气毒物。具体来讲，法案要求EPA，

辨识所有引起“严重的不可逆疾病甚或死亡”的污染物。

制定标准以降低此类污染物的排放，使其达到对公众具有“充分宽余安全边际”的水平。


While attempting to control air toxics during the 1970s and 1980s, EPA became involved in many legal, scientific, and policy debates over which pollutants to regulate and how stringently to regulate them. Debates focused on risk assessment methods and assumptions, the amount of health risk data needed to justify regulation, analyses of the costs to industry and benefits to human health and the environment, and decisions about “how safe is safe.”

70、80年代试图控制空气毒物的过程中，EPA参与了很多法律、科研、政策方面的辩论以确定哪些污染物需要管控、应该管得多严等等。各种辩论纠结于风险评估方法与前提假设，满足立法要求所需的健康风险数据量，分析工业界付出的成本及人与环境得到的收益，还有判定“多安全才算安全”。

 

During this time, EPA was still developing methods to assess risk. These methods were essential tools that would be needed to establish the scientific basis for making risk-based decisions about air toxics. While EPA and the scientific community gained valuable knowledge about risk assessment methods through this work, the chemical-by-chemical regulatory approach—an approach based solely on risk—proved difficult. In fact, in 20 years, EPA regulated only seven pollutants (asbestos, benzene, beryllium, inorganic arsenic, mercury, radionuclides, and vinyl chloride). Collectively, these standards cut annual air toxics emissions by an estimated 125,000 tons.

这一时期，EPA还是不断制定了各种方法以评估风险。这些方法当时作为基础工具用以建立科学基准来对空气毒物进行“风险为准”的判定。尽管EPA和科学界通过这一工作对风险评估方法获得了宝贵的知识，但针对逐个化学品立法的方法 – 即只查风险方法 – 证明是行不通的。事实上，EPA在二十年里只规范了七种污染物 (石棉、苯、铍、无机砷、汞、放射性同位素、以及氯乙烯)。总体来说，这些标准还是削减了年空气毒物排放约125,000吨。

The 1990 Clean Air Act Amendments:

A “Technology First, Then Risk” Approach

Realizing the limitations of a chemical-by-chemical decision framework based solely on risk, and acknowledging the gaps in scientific and analytical information, Congress adopted a new strategy in 1990, when the Clean Air Act was amended. Specifically, Congress revised Section 112 of the Clean Air Act to mandate a more practical approach to reducing emissions of toxic air pollutants.

1990年清洁空气法修正案

“先技术，后风险”方法

意识到逐个化学品只看风险判定框架的局限性，也承认科学与分析信息的差距，国会在修改清洁空气法规程中，于1990年采用了新的策略。具体来讲，国会修改了清洁空气法112节内容，授权了更实际的方法以减少有毒空气污染物的排放。

 

This approach has two components. In the first phase, EPA develops regulations - MACT (Maximum Achievable Control Technology) standards - requiring sources to meet specific emissions limits that are based on emissions levels already being achieved by many similar sources in the country. Even in its earliest stages, this new “technology-based” approach clearly produced real, measurable reductions. In the second phase, EPA applies a risk-based approach to assess how these technology-based emissions limits are reducing health and environmental risks. Based on this assessment, EPA may implement additional standards to address any significant remaining, or residual, health or environmental risks. EPA completed development of its strategy for addressing residual risks from air toxics in March of 1999.

这一方法包含两个部分。第一阶段，EPA制定规则 – MACT(最大可及控制技术)标准 – 要求排放源达到特定的排放限值，即国内其它类似排放源已达到的排放水平。这种新的“技术为本”的方法即使在其最初阶段就取得了实在的、可量化的减排效果。第二阶段，EPA 采用“风险为准”的方法评估这些基于技术的排放限值如何降低健康与环境风险。在此评估基础上，EPA 可以实施进一步的标准以处置其它显著的剩余、残余的健康环境风险。EPA在1999年3月完成制定了这一策略，以处置空气毒物剩余的风险。

 

 

WHAT PROGRESS HAS BEEN MADE IN REDUCING TOXIC AIR POLLUTION?

As of August 2000, EPA has issued 45 air toxics MACT standards under Section 112 of the Clean Air Act Amendments. These standards affect 82 categories of major industrial sources, such as chemical plants, oil refineries, aerospace manufacturers, and steel mills, as well as eight categories of smaller sources, such as dry cleaners, commercial sterilizers, secondary lead smelters, and chromium electroplating facilities. EPA has also issued two standards under Section 129 of the Clean Air Act to control emissions, including certain toxic pollutants, from solid waste combustion facilities (one standard for municipal waste combustors and the other for medical waste incinerators). Together, these standards reduce emissions of over 100 different air toxics. When fully implemented, all of these standards will reduce air toxics emissions by about 1.5 million tons per year - almost 15 times the reductions achieved prior to 1990. Each of the final rules developed since 1990 is summarized in an appendix to this document (pages 9 to 31). These summaries describe the sources for which final rules have been issued as of August 2000, the types of pollutants the sources emit, and how EPA’s rules are reducing their emissions.

减少空气毒物工作取得了哪些进展？

到2000年8月，EPA根据清洁空气法修正案112节要求发布了45项空气毒物MACT标准。这些标准涉及主要工业排放源中的82个类别，比如化工厂、炼油厂、航空制造、钢铁厂、以及8个次要排放源类别，比如干洗业、商用消毒业、二级熔铅行业、镀铬业等。EPA还根据清洁空气法129节要求颁布了两项标准用以控制排放，包括某些固废焚烧厂的有毒空气污染物(一项针对城市废物焚烧装置，另一项针对医用废弃物焚烧炉)。汇总起来，这些标准涉及过百种空气毒物的减排。如能完全实施，所有这些标准可以每年减少约150万吨空气毒物的排放 – 几乎是1990年以前减排量的15倍。

 

Some of these air toxics rules have the added benefit of reducing ground-level ozone (urban smog) and particulate matter. This occurs because some air toxics are also smog-causing volatile organic compounds (VOCs) (e.g., toluene) or particulate matter (e.g., chromium). In addition, some of the technologies and practices designed to control air toxics also reduce VOCs or types of particulate matter that are not currently among the 188 listed air toxics. Reductions of smog-causing pollutants and particulate matter are important because of the health and environmental problems they can cause. Most notably, urban smog can cause respiratory problems and can damage vegetation, and particulate matter can cause many detrimental impacts on human health, such as bronchitis, lung damage, increased infection, aggravation of asthma, and premature death. In addition many of these pollutants can contribute significantly to impaired visibility in places, such as national parks, that are valued for their scenic views and recreational opportunities.

部分空气毒物规定有助于减少地面臭氧(城市污霾)和颗粒物。主要因为有些空气毒物也属于引发污霾的挥发性有机物(VOC) (比如甲苯)或颗粒物(比如铬)。此外，有些用于控制空气毒物的技术和做法也有助于减少目前尚未计入188种空气毒物的挥发性有机物(VOC)或颗粒物。减少引发污霾的污染物和颗粒物确属必要，主要因为其造成的健康和环境问题。尤其值得注意，城市污霾也能引发呼吸问题、破坏植被、对人类健康造成不利影响，比如支气管炎、肺部损害、增加感染、加重哮喘、以及早逝等。此外，此类污染物还显著降低各地的能见度，比如国家公园，而这些地方的价值正在于其景观和休闲活动。

 

EPA has consistently worked to develop air toxics standards that achieve the required reductions in air pollution while providing regulated communities with as much flexibility as possible in deciding how to comply with the standards. For example, under a flexible regulation, industries may reduce their emissions by redesigning their processes, capturing and recycling emissions, changing work practices, or installing any of a variety of control technologies. Flexibility helps industries minimize the cost of compliance and encourages pollution prevention. To provide flexibility, EPA makes every effort to develop standards that are based on performance measures rather than specific control devices, and that allow for equivalent alternative control measures.

EPA既持续努力制定空气毒物标准以达到减排目标又为所监管的区域或行业提供尽可能的灵活性，使其可以自选满足标准的方式方法。例如，在条例的灵活性下，业界可以通过重新设计工艺、或收集循环排放物、或改变作业工艺、或采用任一可选的控排技术，以减少排放。灵活性有助于业界降低合规成本并鼓励污染防治。为确保灵活性，EPA尽量制定基于效力评估而非特定控排装置的标准，尽量兼容同等可代换的控排措施。