While poor air quality is generally associated with adverse health outcomes, some air pollutants are more harmful than others. In this blog, Dr Nicholas Marsden outlines the need for building air quality monitoring networks to study specific properties of fine particulate matter (PM).

• Some PM types are more harmful than others; more research on PM properties is essential to regulate the source and exposure to harmful PM types.
• Air quality monitors that measure PM composition and properties across industrial, public and domestic settings are needed to build an effective monitoring network.
• Governments should incentivise instrument manufacturers to invest in low-cost air quality monitors that capture data on real-time PM composition, which can be used to inform future air quality legislation.

There is a long-established link between poor air quality and negative health outcomes such as cardiovascular disease, respiratory disease and impaired immune system. However, the actual clinical mechanisms which lead to disease are not well understood. This is a significant problem when examining the causal link between high concentrations of fine particulate matter (PM) and respiratory disease. There is a huge volume of environmental data available that enables the correlation between high concentrations of PM and the occurrence of certain disease in the community. However, the term ‘PM’ encompasses a wide range of pollutants of varying composition, size and particle mixing states. The simplification could be very detrimental to understanding and reducing the health impacts of air pollution.

Lessons from the automotive industry

In recent years, there have been successful campaigns to reduce exhaust emissions from vehicles. This has occurred in an industry that is well regulated and uses similar technologies – combustion engines that use a common fuel type. The amount of diesel and petrol consumed and the characteristics of vehicle fleets is well known. The effectiveness of regulation to reduce emissions can be accurately modelled and verified with ambient measurements. This is done in the current framework of reducing NOx and PM, as well as CO2 for climate change.

Air quality at a particular location is a consequence of a complex interaction of local and regional emissions, meteorological conditions and atmospheric processes that transform the primary emissions both chemically and physically. For example, volatile organic compounds (VOC) emitted from vehicle exhausts are transformed to secondary organic aerosol by condensation and oxidation in the atmosphere. Consequently, it is difficult to attribute poor air quality at a certain location on a particular day to a particular source. However, because vehicle exhaust emissions are ubiquitous in the environment and sufficiently long lived, there is a clear path from reducing emissions to improving air quality.

Whilst the effort to reduce PM for vehicle exhaust emission can be viewed as relatively successful, the poor health outcomes associated with air quality will not end with the reduction in traffic emissions. Domestic and industrial consumption of solvents and chemicals is increasing rapidly and becoming the dominant source of VOC in the environment, as vehicle exhaust emissions continue to decline. Additionally, the routes to exposure are more diverse, ranging from exposure in the workplace to exposure in the home. This represents a different challenge as it involves a much wider range of industries. If we are to develop resilient solutions that combat poor air quality without significantly impacting industrial competitiveness and consumer choice, the rather blunt tool of reducing all PM will not be sufficient.

Not all PM is created equal

The key to effective regulation of air quality in the future environment is understanding that all PM is not equal; some types are more harmful than others. For example, primary aerosol emitted from vehicles contain trace metals and are likely to be more harmful than the secondary organic aerosol derived from natural vegetation. The sources, exposure routes and toxicity of the more harmful types are not well understood, partly because measuring aerosol properties is very challenging. Currently, long term monitoring of PM composition is only carried out at specialist research sites such as the supersites at Birmingham, London and Manchester and use techniques that are expensive and require expert operators. Linking the harmful aspects of specific sources of PM to adverse effects in the human body requires complex experiments involving multi-disciplinary teams of medical, clinical and aerosol scientists.

More of these types of experiments are needed if we are to gain a better understanding of the specific properties of PM that are harmful. This will inevitably lead to the next challenge: how to efficiently regulate the source and exposure of a new set of PM properties in industry and the wider environment. Such regulation can only be introduced if an effective monitoring network is available.

Building a resilient and effective PM monitoring network

The current monitoring network is built around established technology that reliably reports PM concentration in relatively small number of locations. The future economy will require simplified, commercially available instrumentation that is capable of monitoring PM composition in a much wider network that covers industrial, domestic and public settings.

Recently, a multitude of low-cost air quality monitors have become commercially available. These products offer the opportunity to measure current air quality metrics such as PM2.5, PM10 in a more diverse set of environments than traditional air quality monitoring networks. However, these instruments do not make measurements that meet the requirements of the monitoring certification scheme (MCERTS) and do not measure the PM composition that will be required for future improvements in air quality. A new generation of instruments is required that can monitor PM composition in real-time without the need for expert operators. Fundamental to achieving this will be government incentives to enable instrument manufacturers to make the long term investment in product development for MCERTS standard applications.

Although PM pollution can be greatly reduced, it cannot be eliminated entirely: most human activity creates it and a great deal of it is natural. The challenge is how we eliminate the most harmful PM without placing an unnecessary burden on industry or reducing consumer choice. Future legislation must specifically target the producers of harmful PM. The answer lies with technology.

This article was originally published in On Air Quality, a collection of thought leadership pieces and expert analysis on how to tackle air pollution, published by Policy@Manchester.

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