Air quality index

Children, the elderly and individuals with respiratory or cardiovascular problems are typically the first groups affected by poor air quality.

When the AQI is high, governmental bodies generally encourage people to reduce physical activity outdoors, or even avoid going out altogether.

When wildfires result in a high AQI, the use of a mask (such as an N95 respirator) outdoors and an air purifier (incorporating both HEPA and activated carbon filters) indoors are also encouraged.

For example, during rush hour traffic or when there is an upwind forest fire or from a lack of dilution of air pollutants.

[7] On a day when the AQI is predicted to be elevated due to fine particle pollution, an agency or public health organization might: During a period of very poor air quality, such as an air pollution episode, when the AQI indicates that acute exposure may cause significant harm to the public health, agencies may invoke emergency plans that allow them to order major emitters (such as coal burning industries) to curtail emissions until the hazardous conditions abate.

Across Australia, a consistent approach is taken with air quality indexes, using a simple linear scale where 100 represents the maximum concentration standard for each pollutant, as set by the NEPM.

There are six AQI bands, with health advice for each: Everyone: Cut back or reschedule strenuous outdoor activities Everyone: Significantly cut back on outdoor physical activities Air quality in Canada has been reported for many years with provincial air quality indices (AQIs).

Significantly, AQI values reflect air quality management objectives, which are based on the lowest achievable emissions rate, rather than exclusive concern for human health.

The AQHI provides a number from 1 to 10+ to indicate the level of health risk associated with local air quality.

For any given hour the AQHI is calculated from the sum of the percentage excess risk of daily hospital admissions attributable to the 3-hour moving average concentrations of these four pollutants.

The AQI level is based on the level of six atmospheric pollutants, namely sulfur dioxide (SO2), nitrogen dioxide (NO2), suspended particulates smaller than 10 μm in aerodynamic diameter (PM10),[19] suspended particulates smaller than 2.5 μm in aerodynamic diameter (PM2.5),[19] carbon monoxide (CO), and ozone (O3) measured at the monitoring stations throughout each city.

The main aim of the CAQI was to have an index that would encourage wide comparison across the EU, without replacing local indices.

[22] Some of the key pollutant concentrations in μg/m3 for the hourly background index, the corresponding sub-indices, and five CAQI ranges and verbal descriptions are as follows.

[22] The National Air Quality Index (NAQI) was launched in New Delhi on September 17, 2014, under the Swachh Bharat Abhiyan.

[25][26][27][28] The highest AQI in India was recorded in New Delhi on 18th November 2024 with it being 1,081 and the concentration of PM2.5 - particulate matter measuring 2.5 microns or less in diameter that can be carried into lungs, causing deadly diseases and cardiac issues.

[31] The continuous monitoring systems that provide data on near real-time basis are installed in New Delhi, Mumbai, Pune, Kolkata and Ahmedabad.

The proposed NAQI will consider eight pollutants PM10, PM2.5, NO2, SO2, CO, O3, NH3, and Pb) for which short-term (up to 24-hourly averaging period) National Ambient Air Quality Standards are prescribed.

[33] Based on the measured ambient concentrations, corresponding standards and likely health impact, a sub-index is calculated for each of these pollutants.

Likely health impacts for different NAQI categories and pollutants have also been suggested, with primary inputs from the medical experts in the group.

[citation needed] Singapore uses the Pollutant Standards Index to report on its air quality,[34] with details of the calculation similar but not identical to those used in Malaysia and Hong Kong.

[35] The PSI chart below is grouped by index values and descriptors, according to the National Environment Agency.

The index aims to help the public easily understand the air quality and protect people's health.

The EPA has established National Ambient Air Quality Standards (NAAQS) for each of these pollutants in order to protect public health.

where: The EPA's table of breakpoints is:[42][43][44][45][46] 8-hr 1-hr 24-hr 24-hr 8-hr 1-hr; 24-hr 1-hr Category Suppose a monitor records a 24-hour average fine particle (PM2.5) concentration of 26.4 micrograms per cubic meter.

The equation above results in an AQI of: which rounds to index value of 83, corresponding to air quality in the "Moderate" range.

[48] If multiple pollutants are measured at a monitoring site, then the largest or "dominant" AQI value is reported for the location.

To accurately reflect the current air quality, the multi-hour average used for the AQI computation should be centered on the current time, but as concentrations of future hours are unknown and are difficult to estimate accurately, EPA uses surrogate concentrations to estimate these multi-hour averages.

[52] Historical air monitoring data including AQI charts and maps are available at EPA's AirData website.

[54] Subscribers get notifications about the changes in the AQI values for the selected location (e.g. home address), based on air quality conditions.

While the methodology was designed to be robust, the practical application for all metropolitan areas proved to be inconsistent due to the paucity of ambient air quality monitoring data, lack of agreement on weighting factors, and non-uniformity of air quality standards across geographical and political boundaries.