Ambient air quality criteria, or standards, are concentrations of pollutants in the air, and typically refer to outdoor air. The criteria are specified for a variety of reasons including for the protection of human health, buildings, crops, vegetation, ecosystems, as well as for planning and other purposes. There is no internationally accepted definition but usually "standards" have some legal or enforcement aspect, whereas "guidelines" may not be backed by laws. "Criteria/criterion" can be used as a generic term to cover standards and guidelines.
Various organisations have proposed criteria e.g. WHO, EU, US EPA. These criteria are often similar – but not always, even if they are proposed for the same purpose (e.g. the protection of human health).
Specifying the criteria It is important for any numerical standard that averaging period, unit, and statistical measure are given (e.g. the 98th percentile of hourly means measured over a calendar year in micrograms per cubic metre (μg/m3)). Without these there is no common ground for a given criterion, making it confusing or even meaningless. Criteria can be set in different units (e.g. μg/m3, parts per billion by volume (ppbv), parts per billion by mass (ppb (mass)), parts per million (ppm)) and it is possible to convert between all of these units if the molecular mass of the pollutant and the temperature are known. Different standard temperatures are used throughout the world and so it is important to state the temperature of conversion (if relevant). Most pollutants have ambient criteria in the parts per billion (ppb) or μg/m3 range. Some have smaller units (e.g. dioxins are often in picograms/m3); others have larger units (e.g. carbon monoxide (CO) in mg/m3). Particle pollution (e.g. PM10, PM1.0) is specified in units of mass (e.g. μg/m3) and not in units of volume (ppmv).
In the EU, the pollutants and their criteria are specified in Directive 2008/50/EC.
The criteria Below is a list of available air quality criteria around the world. There is a lot of cross referencing between organizations (e.g. the International Finance Corp (IFC)) that have their own criteria but ultimately, many criteria are based on those specified by the World Health Organization (WHO). It is important when complying with ambient air quality criteria to check the direct reference as well. Not all related caveats/controlling parameters of a criterion can be put in the table, and therefore those specified below are mostly those that most monitoring agencies specify. These agencies also list whether criteria must be monitored in a specific way to fit with compliance measures. PollutantAbbr.ValueUnitsAveraging PeriodStatistical Measure# exceedencesOrganisationStatusApplicabilityNotesNitrogen dioxideNO240μg/m3Annual1MeanNoneWHO Air quality guidelines - global update 2005 www.who.int/phe/health_topics/outdoorair/outdoorair_aqg/en/GuidelineGlobalNitrogen dioxideNO2200μg/m31 hourMeanNoneWHO GuidelineGlobalNitrogen dioxideNO240μg/m3AnnualMeanNoneEU Limit ValueEU Member StatesCalendar YearNitrogen dioxideNO253ppbAnnualMeanNoneUS EPALegalUnited StatesPrimary and SecondaryNitrogen dioxideNO2100μg/m3AnnualYrly mean of dailyNoneSCENR Supreme Council for Environment and Natural Resources, Executive Bye-law for the Environment Protection Law Issued via the Decree Law No. 30 for the Year 2002, Annex 3"LegalQatarCalendar YearNitrogen dioxideNO240μg/m3AnnualMeanNoneChinese Ministry of Ecology and EnvironmentLegalChinaNitrogen dioxideNO2100μg/m3DailyMeanNew Zealand Ministry for the EnvironmentGuidelineNew ZealandCalendar YearNitrogen dioxideNO2113μg/m3DailyDaily mean of hourlyNoneJapanese Ministry of Environment Japanese Ministry of Environment, Environmental Quality Standards - Air Quality https://www.env.go.jp/en/air/aq/aq.htmlLegalJapanQuoted as 0.06 ppmNitrogen dioxideNO2150μg/m3Daily99.7%ile1 day/yrSCENR LegalQatarCalendar YearNitrogen dioxideNO280μg/m3DailyMeanNoneChinese Ministry of Ecology and EnvironmentLegalChinaNitrogen dioxideNO2100ppb1 hour98% of 1-hour daily maximum concentrations, averaged over 3 yearsNoneUS EPALegalUnited StatesPrimaryNitrogen dioxideNO240μg/m3AnnualMeanNoneIndia Central Pollution Control Board (CPCB) India Central Pollution Control Board - Air Quality Standards http://cpcb.nic.in/air-quality-standard/LegalIndiaCalendar YearNitrogen dioxideNO230μg/m3AnnualMeanNoneIndia Central Pollution Control Board(CPCB) LegalIndia - Ecologically sensitive areasCalendar YearNitrogen dioxideNO280μg/m324 hour2MeanNoneIndia Central Pollution Control Board (CPCB) LegalIndiaCalendar YearNitrogen dioxideNO2200μg/m31 hour99.79%ile18 hrs/yrEU Limit valueEU Member StatesCalendar YearNitrogen dioxideNO2200μg/m31 hourMean9/yrNew Zealand Ministry for the EnvironmentLegalNew ZealandCalendar YearNitrogen dioxideNO2400μg/m31 hour99.7%ile26 hrs/yrSCENR LegalQatarCalendar YearNitrogen dioxideNO2200μg/m31 hourMeanNoneChinese Ministry of Ecology and EnvironmentLegalChina PollutantAbbr.ValueUnitsAveraging PeriodStatistical Measure# exceedencesOrganisationStatusApplicabilityNotesSulphur dioxideSO275ppb1 hour99% of 1-hour daily maximum concentrations, averaged over 3 yearsNoneUS EPALegalUnited States*PrimarySulphur dioxideSO2500ppb3 hoursMeanOnce per yearUS EPALegalUnited StatesSecondary quoted as 0.5 ppmSulphur dioxideSO220μg/m3AnnualMeanNoneChinese Ministry of Ecology and EnvironmentLegalChina Category 1 AreasSulphur dioxideSO260μg/m3AnnualMeanNoneChinese Ministry of Ecology and EnvironmentLegalChina Category 2 AreasSulphur dioxideSO250μg/m3DailyMeanNoneChinese Ministry of Ecology and EnvironmentLegalChina Category 1 AreasSulphur dioxideSO220μg/m3AnnualMeanNoneIndia Central Pollution Control Board (CPCB) LegalIndia - Ecologically sensitive areasSulphur dioxideSO250μg/m3AnnualMeanNoneIndia Central Pollution Control Board (CPCB) LegalIndiaSulphur dioxideSO280μg/m324 hourMeanNoneIndia Central Pollution Control Board (CPCB) LegalIndiaSulphur dioxideSO2150μg/m3DailyMeanNoneChinese Ministry of Ecology and EnvironmentLegalChina Category 2 AreasSulphur dioxideSO2150μg/m31 hourMeanNoneChinese Ministry of Ecology and EnvironmentLegalChina Category 1 AreasSulphur dioxideSO2500μg/m31 hourMeanNoneChinese Ministry of Ecology and EnvironmentLegalChina Category 2 AreasSulphur dioxideSO2125μg/m324 hourAny 24 hour periodNoneWHO Interim Target (IT) 1GlobalWas the guideline in 2000Sulphur dioxideSO250μg/m324 hourAny 24 hour periodNoneWHO Interim Target (IT) 2GlobalCalendar Year (1 Jan – 31 Dec)Sulphur dioxideSO2125μg/m324 hourAny 24 hour meanNoneWHO Interim Target (IT) 1GlobalSulphur dioxideSO250μg/m324 hourAny 24 hour meanNoneWHO Interim Target (IT) 2GlobalSulphur dioxideSO220μg/m324 hourAny 24 hour meanNoneWHO GuidelineGlobalSulphur dioxideSO2500μg/m310 minuteAny 10 minute meanNoneWHO GuidelineGlobalSulphur dioxideSO21300μg/m31 hour99.99%ile1 hr/yearRas LaffanLegalQatarCalendar YearSulphur dioxideSO2350μg/m31 hourMean9/yrNew Zealand Ministry for the EnvironmentLegalNew ZealandSulphur dioxideSO2570μg/m31 hourMeanNoneNew Zealand Ministry for the EnvironmentLegalNew ZealandSulphur dioxideSO2120μg/m324 hourAverageNew Zealand Ministry for the EnvironmentGuidelineNew Zealand Abbr.ValueUnitsAveraging PeriodStatistical Measure# exceedencesOrganisationStatusApplicabilityNotesPM10 "Coarse Particulate Matter"150μg/m324 hourAverage over 3 yearsOnce per yearUS EPALegalUnited StatesPrimary and SecondaryPM10125μg/m324 hour99th %ile3 days/yrWHO GuidelineGlobalPM1050μg/m324 hourMeanNoneWHO GuidelineGlobalPM1020μg/m3AnnualMeanNoneWHO GuidelineGlobalPM1060μg/m3AnnualMeanNoneIndia Central Pollution Control Board (CPCB) LegalIndiaPM1010μg/m324 hourMeanNoneIndia Central Pollution Control Board (CPCB) LegalIndiaPM1050μg/m324 hourMean1/yrNew Zealand Ministry for the EnvironmentLegalNew ZealandPM1040μg/m3AnnualMeanNoneChinese Ministry of Ecology and EnvironmentLegalChina Category 1 AreasPM1070μg/m3AnnualMeanNoneChinese Ministry of Ecology and EnvironmentLegalChina Category 2 AreasPM1050μg/m324 hourMeanNoneChinese Ministry of Ecology and EnvironmentLegalChina Category 1 AreasPM10150μg/m324 hourMeanNoneChinese Ministry of Ecology and EnvironmentLegalChina Category 2 AreasPM2.5 "Fine Particulate Matter"35μg/m324 hour98% averaged over 3 yearsNoneUS EPALegalUnited StatesPrimary and SecondaryPM2.525μg/m324 hourAny 24 hr meanNoneWHO GuidelineGlobalPM2.560μg/m324 hourmeanNoneIndia Central Pollution Control Board (CPCB) LegalIndiaPM2.540μg/m3AnnualMeanNoneIndia Central Pollution Control Board (CPCB) LegalGlobalPM2.575μg/m324 hourAny 24 hr meanNoneWHO Interim target (IT) 1GlobalPM2.550μg/m324 hourAny 24 hr meanNoneWHO Interim target (IT) 2GlobalPM2.537.5μg/m324 hourAny 24 hr meanNoneWHO Interim target (IT) 3GlobalPM2.512.0μg/m3AnnualAnnual mean over 3 yearsNoneUS EPALegalUnited StatesPrimaryPM2.515μg/m3AnnualMeanNoneChinese Ministry of Ecology and EnvironmentLegalChina Category 1 AreasPM2.535μg/m3AnnualMeanNoneChinese Ministry of Ecology and EnvironmentLegalChina Category 2 AreasPM2.515.0μg/m3AnnualAnnual mean over 3 yearsNoneUS EPALegalUnited StatesSecondaryPM2.510μg/m3AnnualMeanNoneWHO GuidelineGlobalPM2.525μg/m324 hourMeanNoneWHO GuidelineGlobalPM2.525μg/m3AnnualMeanNoneWHO Interim target (IT) 2GlobalPM2.515μg/m3AnnualMeanNoneWHO Interim target (IT) 3GlobalPM2.535μg/m324 hourMeanNoneChinese Ministry of Ecology and EnvironmentLegalChina Category 1 AreasPM2.575μg/m324 hourMeanNoneChinese Ministry of Ecology and EnvironmentLegalChina Category 2 Areas PollutantAbbr.ValueUnitsAveraging PeriodStatistical Measure# exceedencesOrganisationStatusApplicabilityNotesOzoneO30.07ppm8 hoursAnnual 4th highest daily maximum 8-hour concentration, averaged over 3 years3/yrUS EPALegalUnited States*Primary and SecondaryOzoneO3100μg/m38 hoursAny 8 hour meanNoneWHO GuidelineGlobalOzoneO3100μg/m38 hoursMeanNoneIndia Central Pollution Control Board (CPCB) GuidelineIndiaOzoneO3180μg/m31 hourMeanNoneIndia Central Pollution Control Board (CPCB) LegalIndiaOzoneO3160μg/m38 hoursAny 8 hour meanNoneWHO Interim targetGlobalOzoneO3100μg/m38 hoursDaily maximum 8-hour averaged concentrationNoneChinese Ministry of Ecology and EnvironmentLegalChina Category 1 AreasOzoneO3160μg/m38 hoursDaily maximum 8-hour averaged concentrationNoneChinese Ministry of Ecology and EnvironmentLegalChina Category 2 AreasOzoneO3160μg/m31 hourMeanNoneChinese Ministry of Ecology and EnvironmentLegalChina Category 1 AreasOzoneO3200μg/m31 hourMeanNoneChinese Ministry of Ecology and EnvironmentLegalChina Category 2 AreasOzoneO3235μg/m31 hour99.9%8 hrs/yrSCENR LegalQatarCalendar YearOzoneO3120μg/m38 hours99.8%2x8hrs/yrSCENR LegalQatarCalendar YearOzoneO3150μg/m31 hourMeanNoneNew Zealand Ministry for the EnvironmentLegalNew Zealand PollutantAbbr.ValueUnitsAveraging PeriodStatistical Measure# exceedencesOrganisationStatusApplicabilityNotesCarbon monoxideCO35ppm1 hourMean1/yrUS EPALegalUnited StatesPrimaryCarbon monoxideCO40mg/m31 hourMaximumNoneSCENR LegalQatarCalendar YearCarbon monoxideCO4mg/m31 hourMaximumNoneIndia Central Pollution Control Board (CPCB) LegalIndiaCarbon monoxideCO2mg/m38 hourMaximumNoneIndia Central Pollution Control Board (CPCB) LegalIndiaCarbon monoxideCO10mg/m31 hourMeanNoneChinese Ministry of Ecology and EnvironmentLegalChinaCarbon monoxideCO9ppm8 hourMean1/yrUS EPALegalUnited StatesPrimaryCarbon monoxideCO10mg/m38 hourMaximumNoneSCENR LegalQatarCalendar YearCarbon monoxideCO10mg/m38 hourMean1/yrNew Zealand Ministry for the EnvironmentLegalNew ZealandCarbon monoxideCO30mg/m31 hourMean1/yrNew Zealand Ministry for the EnvironmentLegalNew ZealandCarbon monoxideCO4mg/m324 hourMeanNoneChinese Ministry of Ecology and EnvironmentLegalChina