2021 International Day of Clean Air for blue skies

Written by Plistina Almeida and Simon Welchman


This years’ theme to celebrate the International Day of Clean Air for Blue Skies is ‘Healthy Air, Healthy Planet”. As Katestone’s vision is Clear Skies for our clients and communities now and for future generations around the world, we thought we would delve into the real meaning of clean air and clear skies.


We’ll start with the main question: what does clean air mean in general?

Clean air is when air is said to present no harmful levels of pollutants. Epidemiologists and toxicologists study the health effects of air pollutants to determine what levels minimise risks.  Governments use this information to set standards for acceptable levels of air pollutants within their jurisdictions balancing a range of factors including the potential costs and benefits to the community and economy of certain actions.


In Australia, the National Environment Protection (Ambient Air Quality) Measure (AAQ NEPM) published by the National Environment Protection Council (NEPC) with agreement from all State and Territory governments sets the standards for the six key air pollutants to which most Australians are exposed. Whilst the AAQ NEPM standards are principally aimed at evaluating air quality at government-run monitoring stations, they also influence legislation, policy and guidelines issued by State, Territory and Local Governments.


The AAQ NEPM standards for particulate matter are relatively strict in terms of particulate matter (PM10 and PM2.5) in comparison with standards imposed by other countries.  The AAQ NEPM was recently revised to include stricter standards for nitrogen dioxide and sulfur dioxide, making them some of the strictest standards in the world.


So, in order to raise awareness of the campaign #HealthyAirHealthyPlanet, we compiled a few curiosities related to clean air and air quality below and we hope you enjoy this piece of information.


Which air pollutant is most important?

As is often the case, the answer to this question is, it depends.  A sensible way to judge this would be to identify the air pollutant that contributes most significantly to adverse outcomes for human health.


On this measure, PM2.5 is commonly identified as the key air pollutant for adverse health outcomes.

PM2.5 is particulate matter that is less than 2.5 micrometres in diameter, which is less than 3% of the diameter of a human hair. PM2.5 is a common air pollutant that originates from many sources, both natural and manmade.


Sources of PM2.5:

  • natural sources (e.g. bushfire smoke, salt spray)
  • mining
  • industry
  • vehicle exhaust, particularly diesel vehicles
  • solid fuel burning (domestic)
  • secondary formation due to natural and manmade pollutants.


There are well-established links between PM2.5 and human health effects. PM2.5 is considered to be the air pollutant that does the most harm to health. The particulates are so light and small that they tend to stay longer in the air than larger particles.


Does air quality improve at night?

This depends most particularly on the source of air pollutants, which, in many areas of Australia depends on the time of year.


In most urban areas, a key source of air pollutants is motor vehicles.  In these areas, human activity and motor vehicle use gradually diminish after sunset and so do levels of air pollutants.  This is a happy coincidence because at night the atmosphere is more stable and there is generally little or no wind, which means that there is greater potential for elevated levels of air pollutants.


So, if air pollutants are generated at ground level throughout the night, we tend to see higher levels of those air pollutants at night.  A prominent example of this is smoke from wood heaters, which contributes significantly to levels of PM2.5 on winter nights in many cities and towns around Australia.  Most people in Australia will be familiar with the smell of wood smoke in the evening when it starts to get a little chilly.



What time of year is pollution worse?

Winter tends to be the worst season in terms of air pollutants. This happens because temperature inversions are more frequent in winter. Temperature inversions can trap air pollutants close to the ground making it harder for them to disperse.


It’s not by coincidence that people with respiratory problems are more vulnerable to infections during the winter months.


How do we stop or reduce air pollution?

Air pollutants are generated by natural causes such as bushfires, wind-blown dust and salt spray, and man-made activities such as exhausts of fossil-fuelled vehicles and industrial activities.


Nitrogen dioxide (NO2) and PM2.5 are two of the most common air pollutants commonly found in cities around the world. These air pollutants are mainly generated by human activities in cities. For example, in Sydney, nearly 96% of oxides of nitrogen (NOx) and 72% of PM2.5 are due to human activities (NSW EPA, 2019).


Within that, more than 55% of NOx and 12.9% of PM2.5 emissions that are caused by human activities are due to motor vehicle traffic. Domestic solid fuel burning (e.g. wood heaters) make up the majority (more than 50%) of human-induced emissions of PM2.5.


The effect of motor vehicle traffic on air quality is often easy to see in daily plots of monitoring data (especially before the COVID19 pandemic hit us) because our working hours are commonly arranged between mornings and evenings. We, therefore, tend to see a clear pattern with higher levels occurring in the morning and evening with peak traffic volumes.


What can I do to improve air quality?

You might be wondering about what makes air quality worse by now. After the context provided, one has to say that roadside traffic tends to be one of the main contributors to poor air quality within a region. There are obviously other factors that contribute to it:

  • Frequent and long congestions
  • Lack of vegetation buffer next to main roadways
  • Poor vehicle regulation in terms of emissions from exhaust
  • An old fleet.


On the positive side, we can all drive change. Here are some actionable ways for us to reduce air pollution in our everyday lives inspired by the work published by the US EPA (US EPA  2021).

  • Conserving energy at home and at work is possible if we want to.
  • Try looking at the ENERGY RATING label when buying home or office equipment. Choose appliances with more stars.
  • Whenever possible, carpool, take public transportation, ride a bike, or walk.
  • Maintain the proper tuning of your car, boat, and other engines.
  • Check that your tyres are properly filled.
  • When possible, prefer environmentally safe paints and cleaning products.
  • Try to minimise waste by using electronics to the full extent of their life cycles.
  • Get started with mulching or composting leaves and backyard waste.
  • Consider converting your wood heater to a lower emissions form of heating.


Is there any light at the end of the tunnel?

Fortunately, there has been an increased awareness recently in relation to the emission reduction targets in place in most of the countries. This is leading to incentives, educational programs and greater adoption of electric vehicles, which will certainly contribute to a reduction in emissions to the atmosphere.


The IPCC Intergovernmental Panel on Climate Change Sixth Assessment Report (IPCC 6) last month has clearly made a statement: climate change is definitely here. Temperatures are indeed increasing. And unfortunately, global warming is just one of the indications of climate change. Some locations will experience sea level rise, more fire weather days, heavier rainfall and among the effects of these circumstances: more flooding, more waterborne infections, vector-borne diseases and food insecurity.


Emission reductions are paramount to prevent more harmful effects of Climate Change and despite much argument that more policies and thresholds are required, we are able to drive many of the necessary changes and make better choices when it comes to limiting our pollution footprint. Transitioning our economy to a lower carbon future will also improve air quality in many ways.  We’ll address some of these possibilities in future articles here.


How can Katestone help you?

Katestone passionately supports the ethos of clear skies. So much that we made it our vision. Katestone Environmental was created with the aim of contributing to the Australian Environment by providing assessments of the air quality impacts resulting from developments. We assist our clients with the management of air quality, odour, greenhouse gas emissions and climate change associated with planned or existing operations.


Katestone has conducted many studies which involved air pollutant emissions estimation and predicting impacts through state-of-the-art air dispersion modelling, on both a local and regional scale. Coupled with our awareness of the strengths and weaknesses of developments that may impact on the air quality, monitoring equipment, measurement techniques we are in a strong position to both recommend a fit-for-purpose air quality management plan and critically analyse and interpret periodic monitoring data.


Contact us today for Clear Skies.



NSW Environment Protection Authority. 2019. “Air Emissions Inventory for the Greater Metropolitan Region in New South Wales.” Accessed April 22, 2020, https://www.epa.nsw.gov.au/-/media/epa/corporate-site/resources/air/19p1918-air-emissions-inventory-2013-summary.pdf?la=en&hash=59CF67ACA719CD8E06B34356C35A7C172B43640F.

United States Environmental Protection Agency. 2021. “Actions You Can Take to Reduce Air Pollution”. [ONLINE] Accessed September 8, 2021.  https://www3.epa.gov/region1/airquality/reducepollution.html.

National Environment Protection Council. 2021. “Variation to Ambient Air Quality NEPM – ozone, nitrogen dioxide and sulfur dioxide.” [ONLINE] Accessed September 8, 2021. http://www.nepc.gov.au/nepms/ambient-air-quality/variation-ambient-air-quality-nepm-ozone-nitrogen-dioxide-and-sulfur.

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