Causes of the unremitting high ambient levels of PM10 in a suburban background site in NE Spain

Abstract

Atmospheric PM₁₀ and benzo(a)pyrene (BaP) concentrations in Manlleu (NE Spain) have remained high from 2008 to 2023, frequently exceeding EU limit/target values, and reaching BaP levels up to six times higher than urban averages in Spain. Furthermore, PM speciation campaigns were carried out in 2013, 2014-2015, 2016-2017 and 2021-2022. Chemical mass closure for autumn-winter showed a consistent PM₁₀ composition for the different PM speciation campaigns, comprising 46-53% organic matter (OM), 18-26% secondary inorganic aerosol (SIA), 13-23% mineral matter (MM), and 5-9% elemental carbon (EC). Trend analysis revealed very light decrease and constant concentrations for PM₁₀ and BaP, respectively over the study period, emphasizing the need for compliance with current and forthcoming EU air quality directives, the last aiming to halve PM₁₀ limit values. Source apportionment of samples of the sporadic campaigns identified biomass burning (BB, 17.5 μg m^-3, 48%) and MM and industry (16.3 μg m^-3, 44%) as the main autumn-winter PM₁₀ contributors, with high SIA concentrations attributed to several factors, including high ammonia (NH₃) emissions. Local topography and meteorological conditions contribute to aggravate PM₁₀ pollution. While metal concentrations have decreased since 2013, suggesting reduced industrial emissions, persistently high OM and EC concentrations indicate ongoing issues with BB emissions from domestic, commercial, and agricultural sources. Online analysis of black carbon (BC) and non-refractory PM₁ components during winter 2016-2017 confirmed domestic and commercial BB as the primary sources of the BB contributions. These findings highlight the need of the implementation of more effective measures in reducing BB and agricultural/farming NH₃ emissions. This study highlights the relevance of these issues for similar towns, the probable unremitting problem over the last decade, and the necessity of enhanced monitoring in small cities and policy actions to meet air quality standards under the new EU directive.

Keywords: Air quality; Ammonia; Benzo(a)pyrene; Biomass burning; PM(1); PM(10); Source apportionment.