# Coarse particulate matter air pollution in Porto Metropolitan area, Portugal: time series analysis, trends and implications for public policies

## TL;DR

This study analyzes 22 years of PM10 air pollution data in the Porto Metropolitan area, showing a decline followed by stagnation and implications for public health policies.

## Contribution

The study provides a long-term analysis of PM10 trends and spatial variability in an urban region, highlighting policy implications.

## Key findings

- PM10 concentrations declined from the early 2000s to mid-2010s but stagnated or increased afterward.
- Exceedances of WHO air quality guidelines were frequent, especially under the stricter 2021 guideline.
- No significant differences in PM10 levels were found between monitoring station types, suggesting widespread regional exposure.

## Abstract

Air pollution remains a persistent environmental and public health concern in urban regions. This study presents a 22-year analysis (2001–2022) of coarse particulate matter (PM10) concentrations across 15 monitoring stations in the Porto Metropolitan Area (PMA), Portugal. The stations, pre-classified by national authorities as traffic, background-urban, background-suburban, or industrial, were used to assess long-term temporal trends and spatial variability. Annual mean PM10 concentrations were calculated and linear regression was applied to evaluate trends. Differences between station types were tested using statistical analysis. The results revealed consistent decline in PM10 levels from the early 2000s to the mid-2010s, followed by stagnation or increases at several stations in the final years of the series. While higher concentrations were historically observed at traffic and industrial sites, no statistically significant differences in annual mean PM10 concentrations were found between stations of different classifications or within classifications, even when comparing distinct time periods. This homogeneity suggests widespread regional exposure, likely driven by shared emission sources, atmospheric transport, and urban development patterns across the PMA. When compared to World Health Organization (WHO) air quality guidelines, exceedances were frequent and persistent. From 2001 to 2011, nearly all stations with valid data exceeded the 2005 guideline of 20 µg/m3. Between 2012 and 2020, the exceedances gradually decreased, although several stations still surpassed the guideline. However, under the 2021 WHO guideline (15 µg/m3), all stations with valid data for 2021 and 2022 again exceeded the guideline. These findings highlight the need for integrated, long-term air quality policies.

Clinical trial number: Not applicable.

The online version contains supplementary material available at 10.1007/s11356-026-37546-w.