Updates from Environmental Experts

The Ultimate Guide to Understanding Air Quality Data in 2020

Amalia Helen (9)-1

As the world becomes more aware of air pollution on their doorstep, our aim is to make it as easy as possible to find simple answers to the most important air quality data questions of 2020.

1) What Exactly is Air Pollution?

Air pollution is made up both of particles and gases that in high concentration can be harmful to us. There are many different types of air pollutant but six of the most commonly monitored are:

  • Ozone

  • Sulfur Dioxide

  • Carbon Monoxide

  • Nitrogen Dioxide

  • Fine Particulate Matter

  • Fine & Coarse Particulate Matter 

Individual air pollutants are also distinguished in terms of primary (air pollutants directly emitted) and secondary pollutants (not directly emitted but formed when other pollutants react in the atmosphere).


2) Where Does Air Pollution Come From?

Sources of air pollution could be:

a) Man-made such as the air pollution caused by industrial work or traffic. 

b) Natural sources such as dust or mineral ash. 


Pollen as an Air Pollutant

Pollen comes from the male part of many plants’ reproductive system and is produced by any seed-producing plant type, (not just beautiful flowers as many believe). Allergic pollen is produced by specific grass, weeds, or trees, and gets moved around by insects, wind, and water.

Although pollen is considered to be a Particulate, it's a bit larger than the two commonly reported types of Particulate Matter (PM2.5 and PM10) so it's treated a bit differently.

Air Pollution Sources Can be Local or Far Away

Many people assume they will be at risk only while they're next to an industrial plant, bush fire or busy road, but air pollution can also be caused by sources very far away. 

The orange in this video shows mineral dust transported all the way from Sub-Saharan Africa to  South America and the Atlantic: (!)

Credit: Simulating the Transport of Aerosols with GEOS-5, National Aeronautics and Space Administration

Air Pollution Moves Very Quickly

Air quality also changes very quickly - the air you're breathing could vary on an hourly basis and from street to street. Here is a snapshot of changing PM10 levels across London over the course of just a few hours:


3) What is the Impact of Poor Air Quality?

All of us know that air pollution is bad for us, but few of us understand the true scale of impact:

The World's Greatest Environmental Threat to Health

Official statistics from the World Health Organisation state that 92% of us live in areas where air pollution exceeds the guidelines considered to be safe, 9/10 people breathe polluted air each day,  and that 4.2 million premature deaths occur each year as a result of exposure to air pollution. 

Historical Air Pollution

Prolonged and even short-term exposure can particularly harm sensitive groups with pre-existing respiratory or cardiovascular conditions, the elderly, children, and pregnant women, however the stark reality is:

a) No-one is immune to the health impact of air pollution exposure

b) Air pollution exposure affects our bodies from head to toe - research has found air pollution to be linked to cancer, asthma, strokes & dementia, mental health, skin, bones and more. 

Huge Economic Cost 

The cost of air pollution to the global economy is huge. According to the World Bank, it costs us $5 trillion each year in welfare costs and $225 billion in lost income.

Air pollution is so detrimental to national and global economic health that the UN created a new Wealth Index which factors the economic burden of air pollution on national economies. 

4) Which Air Pollutant is Most Harmful to Me?

There is no one catch-all answer to this question because different populations differ from each other and from the general population in how they are impacted by high concentrations of different pollutants. For example, high levels of O3, PM2.5 and PM10 can pose a significant risk to children and pregnant women.


All of the pollutants have the potential to harm us depending on the levels of concentration and our exposure. This means the most straightforward approach to take is often to consider air quality as a whole rather than the individual impact of each pollutant. (This is precisely why AQI indexes were created in the first place!)

5) How is Air Pollution Monitored?

As technology and science progresses, the methods for monitoring air quality is also improving. Here are a few common ways of scientifically measuring the ambient air quality around us:

Governmental Monitoring Stations

The sensors deployed by governments around the world are typically seen as the most reliable source of air quality information. They are extremely expensive piece of equipment (costing up to $150,000 per station) and look like walk-in rooms containing different types of measurement. The stations are set up in specific locations and measure specific pollutants; each different pollutant will require a different monitor. 

AQ MOnitoring station


NASA's earth observing satellites provides information about air quality information from above. The instruments deployed by the satellites observe air quality around the world which is then used by air quality managers and researchers looking to study the impact of air pollution on human health and agriculture. Satellite sources of air quality information can be particularly useful when it comes to understanding the impact and spread of a wildfire from a bird's eye perspective.


Low-Cost Sensors

In recent years, there has been a significant increase in the number of low-cost air quality sensors on the market, ranging in type from stationary to portable. At best, low-cost air quality sensors can provide air quality monitoring of specific pollutants but without the ability to conduct in-depth air quality data analysis or advanced QA, the accuracy of these low-cost air quality sensors is questionable

6) What is an Air Quality Index? (AQI)

BreezoMeter Air Quality Index Gradient

An 'Air Quality Index' is a method used by companies and governments to communicate air quality in an understandable way. The average member of the public will not know what '200pbb' concentration of a particular pollutant means for them, or even if this number is high or low - so instead, the individual pollutant concentrations are taken and translated to an index that helps people understand air quality in a more intuitive way.

Importantly, the index standards and scales used by different countries can be very different. For example, in the USA, the AQI scale ranges from 0-500 while in Hong Kong, it ranges from 1-10.

7) What are the Common Challenges When it Comes to Monitoring Air Quality? 

There are a number of freely available sources of air quality data around the world but as we'll see, the methods used by these data providers are not without problems:

Government Sensors Don't Report in Real-Time

The main purpose of government collected information is usually to inform regulatory planning and understand trends over time - as a result, their information tends to be reported as averages over time. 

Although the information provided by government station sensors is extremely reliable and accurate for their purpose, it was never intended for real-time decision-making.

Most of the time, this information is reported with a delay of several hours - as we've seen, air pollution is extremely dynamic so used directly, the information isn't actionable for the here and now.

The Gaps Between Government Station Sensors

Government sensors are extremely accurate at their precise location but as you can see from these images, there can be huge distances between these stations, affecting the reliability of air quality information at locations where no station is available. 

If you consider the impact of traffic on air pollution, it's easy to understand how the particular location of a station sensor will affect the air quality reading you receive: If your closest sensor is based in a fairly non-industrialized area away from traffic but you live on a busy road, it's unlikely the information you receive will help you understand the precise air quality at your home address.

Stations vs. BreezoMEter

Differences in the Number of Pollutants Measured

Some sensors will monitor  the 6 common air pollutants, maybe even more, while some will monitor 3 and some 5. You can never be sure that you're receiving a comprehensive picture of air quality unless you interrogate the data a little more deeply.

Difficult to Measure Fire Impact

Fires smoke moves extremely quickly and unpredictably which is frequently missed by monitoring stations. A station that's in the vicinity of a station sensor can also take it offline, preventing reliable air quality reporting when residents need it the most.  


Low-Cost Sensors & Lack of Standardization

The readings given by low-cost air quality sensors will differ dramatically depending on where exactly individual sensors are positioned and there is very little ability to control this. For example, the readings for a sensor placed by a busy road will be very different to one based in the middle of a park, making it very difficult to understand the factors contributing to air quality or which readings are likely to be anomalies.

It's also very difficult to confirm whether or not the individual low cost sensors are calibrated as often as they need to be, an extremely important factor when it comes to determining level of accuracy. 

Lastly, the individual reliability of a low-cost sensor will really depend on the particular type and model. For further reading, South Coast AQMD have put together a comprehensive report based on their laboratory evaluation of different low-cost air quality sensors.

8) How Does BreezoMeter’s Technology Work?

BreezoMeter adopts an innovative approach to air quality data reporting to solve the above mentioned challenges.

Multi-Layered Data Approach 

We combine data from multiple data sources, which includes more than 47,000 sensors worldwide, meteorological data, satellites, weather, fire and sandstorm events, and live traffic information. This unique approach means we're able to collect information even when one source becomes unavailable. 

Virtual Sensing 


  • We calculate air pollution in 440 million geographical points around the world.

  • We validate and organize more than 1.8 TB of data each hour.

  • We deploy 35 different algorithms, machine-learning and sophisticated modelling to calculate 7.5 billion pollutant concentrations in high accuracy on an hourly basis.

  • The end result is real-time air quality information that is accurate up to a micro-local scale of 5 meters/16 feet!

 9) How Accurate is BreezoMeter?

We are one of the few air quality data providers committed to ensuring and validating the accuracy of our information on an ongoing basis. In order to do this, we use a Continuous Accuracy Validation process which utilizes the "Leave One Out Cross-Validation Method". 

Essentially, we eliminate one sensor's data from our input and calculate the result at that sensor's specific location. We then compare our output to the actual sensor reading when we have it. 

The above chart shows how we are correct more than 90% of the time in terms of the USA AQI categories we report (i.e. unhealthy, healthy).

10) Why is BreezoMeter's Information Different from My Local Source?

First of all, official information only takes into account the information from government station sensors,. BreezoMeter on the other hand adopts a multi-data approach as explained above.

Secondly, while BreezoMeter also reports information in all local Air Quality Indexes AQIs, we default to a Global Air Quality Index that can be used to understand and compare air pollution wherever you are in the world. 

We created this universal standard - which ranges from 0 (Poor) to 100 (Excellent) to solve for the huge variation in methods and scale deployed by different countries. Our Global AQI is also based on epidemiological studies - it is not biased by any economical or political issues or agendas.

Guide to Evaluating Air Quality Data Provider

11) How Does the Weather Impact Air Quality?

The clear link between air quality and weather is precisely why we use live weather information to help us accurately calculate and predict air pollution. 

Due to a phenomenon called 'wet deposition', rain can help to wash away many of the air pollutants, significantly improving air quality. Similarly, wind can also help to clear the air by preventing air pollutants from concentrating in particular areas.

On the other hand, especially in the case of a wildfire, wind can also unfortunately have the opposite impact by helping to spread toxic smoke. We explain the connection of weather to air quality in much more detail here.


Send Us Your Questions

Do you have a burning air quality related question that we haven't answered? Let us know and we'll do what we can to get it answered here for you.

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