Long-term trends in PM2.5 mass and particle number concentrations in urban air: the impacts of mitigation measures and extreme events due to changing climates

Alma Lorelei de Jesus, Helen Thompson, Luke D. Knibbs, Michal Kowalski, Josef Cyrys, Jarkko V. Niemi, Anu Kousa, Hilkka Timonen, Krista Luoma, Tuukka Petaja, David Beddows, Roy Harrison, Philip K. Hopke, Lidia Morawska

Research output: Contribution to journalArticlepeer-review

13 Citations (Scopus)


Urbanisation and industrialisation led to the increase of ambient particulate matter (PM) concentration. While subsequent regulations may have resulted in the decrease of some PM matrices, the simultaneous changes in climate affecting local meteorological conditions could also have played a role. To gain an insight into this complex matter, this study investigated the long-term trends of two important matrices, the particle mass (PM 2.5) and particle number concentrations (PNC), and the factors that influenced the trends. Mann-Kendall test, Sen's slope estimator, the generalised additive model, seasonal decomposition of time series by LOESS (locally estimated scatterplot smoothing) and the Buishand range test were applied. Both PM 2.5 and PNC showed significant negative monotonic trends (0.03–0.6 μg m −3. yr −1 and 0.40–3.8 × 10 3 particles. cm −3. yr −1, respectively) except Brisbane (+0.1 μg m −3. yr −1 and +53 particles. cm −3. yr −1, respectively). For the period covered in this study, temperature increased (0.03–0.07 °C.yr −1) in all cities except London; precipitation decreased (0.02–1.4 mm. yr −1) except in Helsinki; and wind speed was reduced in Brisbane and Rochester but increased in Helsinki, London and Augsburg. At the change-points, temperature increase in cold cities influenced PNC while shifts in precipitation and wind speed affected PM 2.5. Based on the LOESS trend, extreme events such as dust storms and wildfires resulting from changing climates caused a positive step-change in concentrations, particularly for PM 2.5. In contrast, among the mitigation measures, controlling sulphur in fuels caused a negative step-change, especially for PNC. Policies regarding traffic and fleet management (e.g. low emission zones) that were implemented only in certain areas or in a progressive uptake (e.g. Euro emission standards), resulted to gradual reductions in concentrations. Therefore, as this study has clearly shown that PM 2.5 and PNC were influenced differently by the impacts of the changing climate and by the mitigation measures, both metrics must be considered in urban air quality management.

Original languageEnglish
Article number114500
Number of pages12
JournalEnvironmental Pollution
Issue numberPart A
Early online date2 Apr 2020
Publication statusPublished - Aug 2020


  • PM2.5
  • particle number concentration
  • ultrafine particles
  • mitigation
  • climate variabilities
  • Mitigation
  • Particle number concentration
  • Climate variabilities
  • Ultrafine particles
  • PM

ASJC Scopus subject areas

  • Pollution
  • Health, Toxicology and Mutagenesis
  • Toxicology


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