We look at daily, monthly and annual trends in particulate matter pollution, and highlight bettair® and Enviro Technology’s solution for real-time PM mapping.
Particulate matter (PM) is increasingly recognised as the most dangerous air pollutant to human health. Monitoring PM is therefore a necessity. In this article, we look at how PM pollution changes by the hour, month, year, and across locations, all to demonstrate the importance of continuous PM monitoring. We then present the bettair® PM-only node as the ideal solution for real-time PM mapping.
The problem of particulate matter
Particulate matter describes a huge variety of different substances that are suspended in the air. It is classified according to size, with PM10 consisting of particles up to 10 micrometres in size, and PM2.5 referring to particles 2.5 micrometres or smaller.
Particulate matter is a serious risk to health. Fine, PM2.5 is particularly dangerous as it can be drawn deep into the lungs and can cause respiratory and/or cardiovascular disease. In addition, PM is classified as carcinogenic by the International Agency for Research on Cancer (IARC) and can cause lung cancer.
Recent research estimates that exposure to ambient PM2.5 in the UK led to 48,625 premature adult deaths in 2019.
Monitoring particulate matter
PM is generated by many natural and anthropogenic processes. Natural sources include wind-blown soil and dust, sea spray, and ash from wildfires, whereas the main man-made sources are combustion of fuels (in vehicles, industry, and homes) and other common processes such as tyre and brake wear.
In our article on PM monitoring challenges and how to overcome them, we discussed who should monitor particulate matter. This included:
- The UK government – so that they can assess progress towards meeting their legally-binding air quality targets.
- Local authorities – so that they can support central government in meeting overarching air quality targets, as well as fulfil their obligation to regularly assess air quality in their own areas.
- Facility managers – including those who manage combustion plants, quarries, construction sites, waste processing facilities, and transport hubs.
- Centres supporting children, the elderly, and those with pre-existing health conditions – as these individuals are especially vulnerable to PM pollution.
How does PM pollution change over time?
PM levels do not stay the same over days, weeks, or months – which is why continuous monitoring is crucial. Here, we look at how and why PM pollution changes over time, using data from a study by Harrison and colleagues. While the study is not that recent, the findings remain highly applicable to today.
Daily variation
According to Harrison and colleagues’ hourly data, PM peaks in the early morning as people travel to work. In London and southern and central UK, concentrations then fall in the afternoon. This may be due to greater atmospheric activity during the day, which disperses the pollution, or warmer temperatures leading to the evaporation of volatile compounds, meaning they no longer form PM.
Interestingly, the afternoon drop was not seen in the north of the UK, and this demonstrates that trends from one area cannot necessarily be generalised to another. The researchers link the evening peak to domestic heating and cooking, as well as more stable night-time atmospheric conditions reducing dispersion, and cooler temperatures leading volatile compounds to condense and re-form PM.
Image: Variation of PM2.5 concentrations (µg/m3) at 8 northern and 8 southern UK urban background sites by hour in 2009 (Harrison et al., 2012).
Monthly variation
In Harrison and colleagues’ month-by-month analysis, PM levels were highest from January to April. They attribute this to high levels of heating and stable weather conditions that are non-conducive to the dispersal of pollutants during these months. PM concentrations were lowest during late summer, and it is suggested that this is because warmer temperatures lead to the loss of semi-volatile compounds (like in the afternoon, above).
Concentrations then rise again going into autumn and winter, as people start heating their homes and semi-volatile compounds no longer evaporate in the cooler weather. Again, there were differences between the north and south of the UK. These lay not in the pattern of PM pollution, but in the magnitude of the figures. In London, PM2.5 concentrations ranged from 10 to 22 µg/m3, whereas in the north of the UK, the range was 5 to 14 µg/m3.
Image: Variation of PM2.5 concentrations (µg/m3) at 8 London urban background sites by month in 2009 (Harrison et al., 2012).
Annual trends
Generally, in the UK, PM pollution has been improving year on year. This is demonstrated by the Air Quality Stripes, which are visualisations of annual changes in PM2.5 in different cities since 1850 (we explored the Air Quality Stripes in depth in another blog). Below, you can see that London’s stripes have become blue, indicating improving air quality.
Reasons for improvements may include the introduction of Clean Air Zones, establishment of UK Best Available Techniques (UK BAT) to minimise industrial emissions, and the ban on the sale of smoky coal and restrictions on the sale of wet wood.
However, in a separate graph, you can see that London’s PM2.5 levels still exceed the WHO’s Air Quality Guidelines. Indeed, the Air Quality Stripes creators warn that PM2.5 can have significant health effects even at low levels. The UK government has two legally-binding targets to reduce PM2.5 levels further, under The Environmental Targets (Fine Particulate Matter) (England) Regulations 2023:
- Reduce the annual mean concentration of PM5 in ambient air to 10 µg/m³ or less by the end of 2040.
- Reduce population exposure to PM5 by 35% by the end of 2040, compared to levels between 2016 and 2018.
Image: Annual changes in PM2.5 concentrations in London between 1850 and 2022 (airqualitystripes.info).
Image: London’s PM2.5 levels still exceed the WHO’s Air Quality Guidelines (airqualitystripes.info).
bettair® and Enviro Technology’s solution
Enviro Technology now offer the award-winning bettair® node as a PM-only version, allowing measurement of PM10, PM2.5, and PM1. It has all the same benefits as the original version – being compact, portable, easy-to-use, requiring no-maintenance, and with an accuracy comparable to traditional air quality monitoring stations at a fraction of the price – but allows you to focus on tackling one of today’s most important air pollutants. Use the bettair® PM-only node to collect data in real-time, facilitating continuous or time-sensitive evaluation and management of particulate matter in your area or at your site.
Get in touch with Paul Norman to find out more.
Read more about particulate matter in our other blogs:
- We looked at PM monitoring challenges and how the bettair® PM-only node overcomes them.
- Students responded to PM pollution in these three campaigns.
- We discuss the many ways in which air pollution – including PM – affects children and young adults.
