Abstract
Abstract. The response of particulate matter (PM) concentrations to emission reductions was analysed by assessing the results obtained with two different source apportionment approaches. The brute force (BF) method source impacts, computed at various emission reduction levels using two chemical transport models (CAMx and FARM), were compared with the contributions obtained with the tagged species (TS) approach (CAMx with the PSAT module). The study focused on the main sources of secondary inorganic aerosol precursors in the Po Valley (northern Italy): agriculture, road transport, industry and residential combustion. The interaction terms between different sources obtained from a factor decomposition analysis were used as indicators of non-linear PM10 concentration responses to individual source emission reductions. Moreover, such interaction terms were analysed in light of the free ammonia / total nitrate gas ratio to determine the relationships between the chemical regime and the non-linearity at selected sites. The impacts of the different sources were not proportional to the emission reductions, and such non-linearity was most relevant for 100 % emission reduction levels compared with smaller reduction levels (50 % and 20 %). Such differences between emission reduction levels were connected to the extent to which they modify the chemical regime in the base case. Non-linearity was mainly associated with agriculture and the interaction of this source with road transport and, to a lesser extent, with industry. Actually, the mass concentrations of PM10 allocated to agriculture by the TS and BF approaches were significantly different when a 100 % emission reduction was applied. However, in many situations the non-linearity in PM10 annual average source allocation was negligible, and the TS and BF approaches provided comparable results. PM mass concentrations attributed to the same sources by TS and BF were highly comparable in terms of spatial patterns and quantification of the source allocation for industry, transport and residential combustion. The conclusions obtained in this study for PM10 are also applicable to PM2.5.
Highlights
Air pollution is the main environmental cause of premature death
The highest contributions of all the other remaining sources (OTHER) are observed in the pre-Alpine area and in the Alpine valleys, where the average PM10 levels are lower than the Po Valley
The theoretical analysis carried out by Clappier et al (2017) applying factor decomposition was further developed in this study by undertaking a real source apportionment exercise using chemical transport models (CTMs) models in an area with a complex meteorology and chemistry, namely the Po Valley
Summary
Air pollution is the main environmental cause of premature death. Ambient air pollution caused 4.2 million deaths worldwide in 2016, contributing together with indoor pollution to 7.6 % of all deaths (WHO, 2018). A key element for the design of effective air quality control strategies is the knowledge of the role of different emission sources in determining the ambient concentrations. This is usually referred to as source apportionment (SA) and involves the quantification of the influence of different human activities (e.g. transport, domestic heating, industry, agriculture) and geographical areas (e.g. local, urban, metropolitan areas, countries) to air pollution at a given location.
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