Ambient air quality criteria


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.

Specifying the criteria

It is important for any numerical standard that averaging period, unit, and statistical measure are given. Without these there is no common ground for a given criterion, making it confusing or even meaningless. Criteria can be set in different units, parts per billion by mass, parts per million ) 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. Most pollutants have ambient criteria in the parts per billion or μg/m3 range. Some have smaller units ; others have larger units. Particle pollution is specified in units of mass and not in units of volume.
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 that have their own criteria but ultimately, many criteria are based on those specified by the World Health Organization. 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 six criteria air pollutants 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# exceedencesOrganisationStatusApplicabilityNotes
Nitrogen dioxideNO240μg/m3Annual1Mean-WHOGuidelineGlobal
Nitrogen dioxideNO2200μg/m31 hourMean-WHOGuidelineGlobal
Nitrogen dioxideNO240μg/m3AnnualMean-EU DIRECTIVE 2008/50/EC OF THE EUROPEAN PARLIAMENT AND OF THE COUNCIL of 21 May 2008 on ambient air quality and cleaner air for Europe http://eur-lex.europa.eu/legal-content/EN/TXT/?uri=CELEX:32008L0050Limit ValueEU Member StatesCalendar Year
Nitrogen dioxideNO253ppbAnnualMean-US EPALegalUnited StatesPrimary and Secondary
Nitrogen dioxideNO2100μg/m3AnnualYrly mean of daily-SCENRLegalQatarCalendar Year
Nitrogen dioxideNO240μg/m3AnnualMean-Chinese Ministry of Ecology and EnvironmentLegalChina
Nitrogen dioxideNO2100μg/m3DailyMeanNew Zealand Ministry for the EnvironmentGuidelineNew ZealandCalendar Year
Nitrogen dioxideNO2113μg/m3DailyDaily mean of hourly-Japanese Ministry of EnvironmentLegalJapanQuoted as 0.06 ppm
Nitrogen dioxideNO2150μg/m3Daily99.7%ile1 day/yrSCENRLegalQatarCalendar Year
Nitrogen dioxideNO280μg/m3DailyMean-Chinese Ministry of Ecology and EnvironmentLegalChina
Nitrogen dioxideNO2100ppb1 hour98% of 1-hour daily maximum concentrations, averaged over 3 years-US EPALegalUnited StatesPrimary
Nitrogen dioxideNO240μg/m3AnnualMean-India Central Pollution Control Board LegalIndiaCalendar Year
Nitrogen dioxideNO230μg/m3AnnualMean-India Central Pollution Control BoardLegalIndia - Ecologically sensitive areasCalendar Year
Nitrogen dioxideNO280μg/m324 hour2Mean-India Central Pollution Control Board LegalIndiaCalendar Year
Nitrogen dioxideNO2200μg/m31 hour99.79%ile18 hrs/yrEU Limit valueEU Member StatesCalendar Year
Nitrogen dioxideNO2200μg/m31 hourMean9/yrNew Zealand Ministry for the EnvironmentLegalNew ZealandCalendar Year
Nitrogen dioxideNO2400μg/m31 hour99.7%ile26 hrs/yrSCENRLegalQatarCalendar Year
Nitrogen dioxideNO2200μg/m31 hourMean-Chinese Ministry of Ecology and EnvironmentLegalChina

Abbr.ValueUnitsAveraging PeriodStatistical Measure# exceedencesOrganisationStatusApplicabilityNotes
PM10 "Coarse Particulate Matter"150μg/m324 hourAverage over 3 yearsOnce per yearUS EPALegalUnited StatesPrimary and Secondary
PM10125μg/m324 hour99th %ile3 days/yrWHOGuidelineGlobal
PM1050μg/m324 hourMean-WHOGuidelineGlobal
PM1020μg/m3AnnualMean-WHOGuidelineGlobal
PM1060μg/m3AnnualMean-India Central Pollution Control Board LegalIndia
PM1010μg/m324 hourMean-India Central Pollution Control Board LegalIndia
PM1050μg/m324 hourMean1/yrNew Zealand Ministry for the EnvironmentLegalNew Zealand
PM1040μg/m3AnnualMean-Chinese Ministry of Ecology and EnvironmentLegalChina Category 1 Areas
PM1070μg/m3AnnualMean-Chinese Ministry of Ecology and EnvironmentLegalChina Category 2 Areas
PM1050μg/m324 hourMean-Chinese Ministry of Ecology and EnvironmentLegalChina Category 1 Areas
PM10150μg/m324 hourMean-Chinese Ministry of Ecology and EnvironmentLegalChina Category 2 Areas
PM2.5 "Fine Particulate Matter"35μg/m324 hour98% averaged over 3 years-US EPALegalUnited StatesPrimary and Secondary
PM2.525μg/m324 hourAny 24 hr mean-WHOGuidelineGlobal
PM2.560μg/m324 hourmean-India Central Pollution Control Board LegalIndia
PM2.540μg/m3AnnualMean-India Central Pollution Control Board LegalGlobal
PM2.575μg/m324 hourAny 24 hr mean-WHOInterim target 1Global
PM2.550μg/m324 hourAny 24 hr mean-WHOInterim target 2Global
PM2.537.5μg/m324 hourAny 24 hr mean-WHOInterim target 3Global
PM2.512.0μg/m3AnnualAnnual mean over 3 years-US EPALegalUnited StatesPrimary
PM2.515μg/m3AnnualMean-Chinese Ministry of Ecology and EnvironmentLegalChina Category 1 Areas
PM2.535μg/m3AnnualMean-Chinese Ministry of Ecology and EnvironmentLegalChina Category 2 Areas
PM2.515.0μg/m3AnnualAnnual mean over 3 years-US EPALegalUnited StatesSecondary
PM2.510μg/m3AnnualMean-WHOGuidelineGlobal
PM2.525μg/m324 hourMean-WHOGuidelineGlobal
PM2.525μg/m3AnnualMean-WHOInterim target 2Global
PM2.515μg/m3AnnualMean-WHOInterim target 3Global
PM2.535μg/m324 hourMean-Chinese Ministry of Ecology and EnvironmentLegalChina Category 1 Areas
PM2.575μg/m324 hourMean-Chinese Ministry of Ecology and EnvironmentLegalChina Category 2 Areas

PollutantAbbr.ValueUnitsAveraging PeriodStatistical Measure# exceedencesOrganisationStatusApplicabilityNotes
Carbon monoxideCO35ppm1 hourMean1/yrUS EPALegalUnited StatesPrimary
Carbon monoxideCO40mg/m31 hourMaximum-SCENRLegalQatarCalendar Year
Carbon monoxideCO4mg/m31 hourMaximum-India Central Pollution Control Board LegalIndia
Carbon monoxideCO2mg/m38 hourMaximum-India Central Pollution Control Board LegalIndia
Carbon monoxideCO10mg/m31 hourMean-Chinese Ministry of Ecology and EnvironmentLegalChina
Carbon monoxideCO9ppm8 hourMean1/yrUS EPALegalUnited StatesPrimary
Carbon monoxideCO10mg/m38 hourMaximum-SCENRLegalQatarCalendar Year
Carbon monoxideCO10mg/m38 hourMean1/yrNew Zealand Ministry for the EnvironmentLegalNew Zealand
Carbon monoxideCO30mg/m31 hourMean1/yrNew Zealand Ministry for the EnvironmentLegalNew Zealand
Carbon monoxideCO4mg/m324 hourMean-Chinese Ministry of Ecology and EnvironmentLegalChina

Footnotes

Annual arithmetic mean of a minimum of 104 measurements in a year at a particular site, such as taken twice weekly as uniform 24-hour samples.
24/8/1 hourly monitored values, as applicable, shall be complied with 98% of the time, they may exceed the limits but not on two consecutive days of monitoring.