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19 April 2022
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Understanding Air Pollutants: A Guide to Particulate Matter (PM)

What is Particulate Matter (PM)

Particulate Matter is a mixture of solids and liquid droplets. Some PM is emitted directly, otherwise it forms when pollutants created from various sources react in the atmosphere.

Particulate matter is generally classified in two categories: PM10 and PM2.5.

PM10 refers to particles 10 micrometres or smaller in diameter. PM2.5 refers to smaller particles which are 2.5 micrometres or less in diameter. To put this in perspective, this is 30 times smaller than the average diameter of a human hair (75 micrometres), or 12 times less than pollen.

Sources

Particulate matter comes from both natural and anthropogenic (human caused) sources.

The sources for PM2.5 and PM10 can vary, with much of the PM2.5 found in the air coming from diesel, gasoline and oil combustion emissions. PM10 is often emitted through the dust from construction sites, industrial sources, waste burning, agriculture and landfills.

DEFRA reports the major mobile source of particulate matter (PM) in the UK is road transport, and the main stationary sources are the burning of fuels for industrial, commercial, and domestic purposes. Emissions of dust can also generate high concentrations of particulate matter close to quarries and construction sites.

In London specifically, road transport makes up 30% of PM emissions. Since the introduction of the Ultra Low Emissions Zone (ULEZ) in 2019 vehicular emissions have reduced by 30%, and the proportion of low emitting vehicles has increased significantly. Construction also contributes significantly to PM emissions in London, accounting for 15%.

Environmental Impact

Particulate matter has been shown, in scientific studies by the California Air Resources Board, to reduce visibility, as well as to adversely affect climate, and ecosystems. These effects were clear for all to see during lockdowns across the world in 2020, when views across many of the larger cities became clear for the first time in years.

It is possible for particles to travel long distances with the wind and settle on ground or water, which could lead to effects such as depleting nutrients in soil, making bodies of water acidic and contributing to acid rain effects.

Health Impact

Particle pollution can cause damage to the respiratory system with coarse particles (PM10) irritating the nose, eyes and throat, and fine particles (PM2.5) being even more dangerous, due to their capacity to enter the deeper part of the lungs and even the blood. Any health effect is impacted by the length of time of exposure as well as the size and composition of the particles, with PM2.5 being of the most concern.

Short-term exposure to PM2.5 has been associated with respiratory symptoms, asthma attacks and greater hospital admissions for heart and lung issues. Long term PM2.5 exposure has been linked to reduced lung function in children and premature death in those with chronic lung and heart conditions.

The Global Air Quality Guidelines 2021 from the World Health Organisation (WHO) show that more than 90% of the global population in 2019 lived in areas where particulate concentrations exceeded the 2005 WHO air quality guideline of 10 µg/m3. With reports showing that the annual population-weighted PM2.5 concentrations were highest in the WHO South-East Asia Region, followed by the WHO Eastern Mediterranean Region.

DEFRA have voiced how ‘comprehensive’ action must be taken to safeguard health nationally, and outlined their specific goals to reduce particulate matter emissions by 46% by 2030.

How Can PM Be Measured

There are two methods of measuring particulate matter described by DEFRA, the first is the filter-based gravimetric method. This method involves drawing in a volume of air and weighing the particulate matter to determine the mass in that volume of air.

A second method uses TEOM (Tapered Element Oscillating Microbalance) which involves measuring the change in vibration of a filter to determine PM levels.

The majority of monitoring sites in the UK use TEOM analysers, such as those in the Automatic Urban and Rural Network (AURN).

Sensit by Crowcon RAMP

The RAMP is a robust, remote and reliable low-cost air quality monitoring platform. The device is capable of monitoring up to five gaseous chemical pollutants. The device uses a laser scattering detection method to detect both PM2.5 and PM10 with a range of 1-1000 μg/m3.

The RAMP is suitable for use in a variety of industries including construction, transport, waste, oil and gas, chemical and petrochemical industries.

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