How we calculate our air quality index and why we need it

When it comes to measuring air pollution, raw data is hard to understand. This is why air quality indexes are created. An air quality index (AQI) translates numerical data into a descriptive rating scale and makes it easier for citizens of all ages to understand the level of pollution in the air they breathe.

What is an air quality index?

An air quality index is a scale used to show how polluted the air is, along with the risks associated with each rating. An AQI is calculated using established standards based on medical research for the acceptable levels of major air pollutants.

Air quality indexes serve two main purposes:

  1. To inform the public about air quality in an comprehensible manner so that they may take action to protect their health
  2. To help countries develop and assess policies for better air quality

There are many different air quality indexes used by various government agencies out there. However, none of the AQIs reviewed by us included all relevant air quality parameters for all relevant timeframes. Hence, we created a new AQI to be integrated into our Environmental Intelligence Cloud: one that would encompass all relevant air pollutants at every feasible time frame.

What sets Breeze Technologies’ air quality index apart from the rest?

Our air quality index is based on the official specifications and recommendations of various environmental authorities, including the World Health Organization (WHO), the EU Air Quality Directive, the EU Common Air Quality Index (CAQI), as well as the AQIs of several cities. We had several requirements when creating our AQI:

Completeness: Integrate as many air pollutants as possible

While the majority of AQIs evaluate only a subset of ozone (O3), particulate matter (PM), nitrogen dioxide (NO2), sulphur dioxide (SO2), carbon monoxide (CO), and volatile organic compounds (VOCs), Breeze Technologies’ air quality index covers them all, even adding ammonia (NH3) to the list.

The inclusion of ammonia is due to its ability to form particulate matter, of which the risks are higher in rural areas, where the gas is generated from fertilizer production and livestock waste management in agricultural industries.

Applicability: Evaluate air quality on all possible time scales

Other air quality indexes evaluate air pollution concentrations on time scales of either 1 hour, 8 hours, or 24 hours (aggregating measurements and rating the respective averages). Breeze Technologies takes it one step further by utilizing all three common timeframes (the 8-hour timeframe is currently only used for the evaluation of carbon monoxide concentrations, please refer to the dedicated paragraph below).

While it may be acceptable for individuals to be exposed to a higher concentration of certain pollutants for a short time, this may not be the case in the long run. Because of that pollution thresholds may vary between different time scales; the overall air quality index for a full day may be worse than each individual hourly air quality index. Average measurement benchmarks for 1-hour, 8-hour, and 24-hour intervals provide more accurate air quality data, which in turn allows individuals and governments to make better health and safety decisions.

Our air quality index is calculated based on averages of all pollutant concentrations measured in a full hour, a full 8 hours, or a full day. To calculate an hourly air quality index, we average at least 90 measured data points of pollution concentration from a full hour (e.g. between 09:00 AM and 10:00 AM). At least 18 hourly averages are used to form a daily average.

There are still some limitations: As there is a current lack of scientific and medical data on the effects different levels of concentration have on human health over different amounts of time, differences between 1-hour, 8-hour, and 24-hour evaluation standards do not exist for all pollutants. We are working with scientists and legislators globally towards completing the evaluation standards for all pollutants and timeframes following scientific rigour and good practice. Currently, only pollution thresholds for particulate matter (PM10 and PM2.5) concentrations differ between the 1-hour and the 24-hour time scale. Based on the scientific status quo, threshold limits are the same for ozone, nitrogen dioxide, sulphur dioxide, ammonia, and volatile organic compounds, regardless of whether they are evaluated on a 1-hour or 24-hour time frame.

Transparency: Make the air quality rating understandable

It is important to be transparent in which pollution levels result in which air quality index rating. The table below shows an overview over the air quality index of Breeze Technologies:

RatingO3 (ug/m³)PM2.5 (ug/m³)PM2.5 (ug/m³)PM10 (ug/m³)PM10 (ug/m³) NO2 (ug/m³) SO2 (ug/m³)CO (mg/m³) CO (mg/m³) NH3 (ug/m³) VOC (index)
Timeframe1h1h24h1h24h1h / 24h1h / 24h1h8h1h / 24h1h / 24h
Calculation methodaverageaverageaverageaverageaveragemax. hourly valuemax. hourly valueaverageaveragemax. hourly valuemax. hourly value
Excellent0 - 500 - 70 - 50 - 120 - 100 - 250 - 250 - 20 - 10 - 30 - 50
Fine50 - 1007 - 155 - 1012 - 2510 - 2025 - 5025 - 502 - 41 - 23 - 7.551 - 100
Moderate100 - 13015 - 3010 - 2025 - 5020 - 3550 - 10050 - 1204 - 82 - 47.5 - 37.5101 - 150
Poor130 - 24030 - 5520 - 2550 - 9035 - 50100 - 200120 - 3508 - 304 - 1037.5 - 15,000151 - 200
Very Poor240 - 38055 - 11025 - 6090 - 18050 - 100200 - 400350 - 50030 - 10010 - 3015,000 - 150,000201 - 300
Severefrom 380from 110from 60from 180from 100from 400from 500from 100from 30from 150,000301 - 500
ExcellentAccording to current research, negative impacts on ecosystems are unlikely.
FineAll values are under the legal health protection limits. Effects on ecosystems can no longer be ruled out.
ModerateThe health protection limits are mostly still met. Effects on ecosystems are increasingly possible.
PoorThe measured values are at the level of health protection limit values. Health impairments of sensitive persons may occur sporadically.
Very PoorThe health protection limits have been exceeded. Health impairments of sensitive persons are possible. The population is increasingly informed about the pollutant situation.
SevereThe measured values are at alarming levels. The health protection thresholds are clearly exceeded. Health impairments of all persons are possible.

The overall air quality index for a certain timeframe is then based on the worst air quality index rating for the individual pollutants. An example: Between 14:00-15:00, pollution levels for nitrogen dioxide, ozone and carbon monoxide were “excellent” (i.e. very low), but particulate matter levels were rated as “average”. Then the overall air quality index for that hourly period would be rated as “average”.

Further considerations for individual pollutants

Certain air pollutants require further consideration in order to create an effective and accurate AQI. These are based on existing scientific guidelines on threshold limits that pose a risk to human health.

Carbon monoxide

The 8-hour averages of carbon monoxide are a special case used only to determine the pollutant’s daily average concentration. Our scientists developed this calculation method due to the current lack of official methodology. Over a 24-hour day, 17 8-hour values for carbon monoxide are calculated, with the highest one selected as the daily CO average for our daily air quality index. The methodology is illustrated with example data below:

Mean Value 10.65000.6500
Mean Value 20.61500.6150
Mean Value 30.63250.6325
Mean Value 40.66130.6613
Mean Value 50.67380.6738
Mean Value 60.68380.6838
Mean Value 70.68000.6800
Mean Value 80.69630.6963
Mean Value 90.64000.6400
Mean Value 100.61250.6125
Mean Value 110.53500.5350
Mean Value 120.54880.5488
Mean Value 130.44500.4450
Mean Value 140.39880.3988
Mean Value 150.43000.4300
Mean Value 160.34630.3463
Mean Value 170.32250.3225
MAX / Daily Mean0.6963

Nitric oxide

While nitric oxide is a major air pollutant, it is not included on our AQI. There is currently no data available on the threshold values of nitric oxide as it rapidly oxidizes with other compounds like oxygen, ozone, and volatile organic compounds in ambient conditions to create nitrogen dioxide. As a result, data on nitrogen dioxide is what is used on our AQI instead.

Particulate matter

Our evaluation of particulate matter data differs from some of the governmentally-run air quality monitoring networks: They often report not real-time particulate matter levels, but a moving (floating) average of pollution levels from the last 24 hours. This means that during times of high emissions, like rush hour, reported data is often much lower than the real pollution levels. Our report about particulate matter levels during New Year’s Eve is a particularly strong case. As we aim to empower municipal governments to react to short-term events and citizens to protect themselves, we report particulate matter levels on an hourly basis.

What is the air quality where I live like?

The current reality is that many cities only have a few air quality monitoring stations, with measurements lacking the relevant information city administrators and citizens need. For this reason, Breeze Technologies has developed a citizen portal where comprehensive and hyperlocal air quality data is being provided for cities around the world. This initiative is funded by cities or sponsored by socially responsible corporates, with sensors installed on public infrastructure, corporate buildings, or on homes volunteered by local residents. If you are interested in taking part, you can check our further information about our air quality monitoring and management solutions or contact us.

Note: This article has been updated in January 2024 to reflect changes we made in the ozone-based calculation of the air quality index.