Airborne particulate matter

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Airborne particulate matter (PM) is a pollutant of concern not only because of its adverse effects on human health but because of its ability to reduce visibility and soil buildings and materials. It can be regarded as a suite of pollutants since PM covers a very wide range of particle sizes and also has a diverse chemical composition. Historically, much of the PM arose from coal burning and was measured as black smoke. However, in the second half of the twentieth century in developed countries, there was a reduction in black smoke emissions from coal burning and PM steadily became dominated by carbonaceous particles from road traffic exhaust and the secondary pollutants, ammonium salts and secondary organic carbon. This is exemplified by the composition of fine
particles (referred to as PM2.5) asmeasured inLondon, Delhi and Beijing. Steadily, as control strategies have addressed the more tractable sources of emissions, so sources previously regarded as unconventional have emerged and have been seen to make a significant contribution to airborne PM concentrations. Among these are non-exhaust particles from road traffic, cooking aerosol and wood smoke. The particle size distribution of airborne PM is hugely diverse, ranging from newly formed particles of a few nanometres in diameter through to particles of tens of micrometres in diameter. There has been a great deal of interest in ultrafine (nano) particles because of suspicions of enhanced toxicity, and as traffic emissions decrease as a source, so regional nucleation processes have become much bigger relative contributors to particle number, but not mass.

This article is part of a discussion meeting issue ‘Air quality, past present and future’.
Original languageEnglish
Article number20190319
Number of pages13
JournalPhilosophical Transactions of the Royal Society A: Mathematical, Physical and Engineering Sciences
Issue number2183
Early online date28 Sept 2020
Publication statusPublished - 30 Oct 2020

Bibliographical note

Funding Information:
Data accessibility. Data supporting this publication are openly available from the UBIRA eData repository at Authors’ contributions. R.M.H. conceived the study, designed the study, coordinated the study and prepared the first draft of the manuscript. Competing interests. I declare I have no competing interests. Funding. This research is supported by the Natural Environment Research Council through the AIRPOLL-Beijing project within the APHH Programme (NE/N007190/1), the Clean Air for London (ClearfLo) project (NE/H003142/1) and the NERC-MRC Air Pollution and Human Health Programme (NE/P016499/1). Acknowledgement. The author expresses thanks to colleagues who contributed to the collection of the data from Beijing (James Brean, David Beddows, Tuan Vu, Zongbo Shi) and Delhi (William Bloss, Salim Alam, Leigh Crilley) and others, and to Ulku Alver Sahin for data processing.

Publisher Copyright:
© 2020 The Authors.


  • PM 10
  • PM 2.5
  • airborne particulate matter
  • particle number
  • source apportionment
  • ultrafine particles

ASJC Scopus subject areas

  • General Mathematics
  • General Engineering
  • General Physics and Astronomy


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