Non-linearity of secondary pollutant formation estimated from emissions data and measured precursor-secondary pollutant relationships

Abstract

In order to predict the impacts of reductions in air pollutant emissions, it is important to know whether secondary pollutant concentrations will decline in direct proportion to the reduction in their precursor, referred to as linearity. Trends in airborne concentrations of nitrate, sulfate, and SOC at sites in southern England are compared with emissions and concentration trends for sulfur dioxide (SO2), oxides of nitrogen (NOx), and non-methane VOC, and show some increased ratios of concentrations to emissions, strongly suggestive of non-linearity in the primary-secondary pollutant relationships for nitrate, but not the other pollutants. Analysis of a further 20-year dataset from the AGANET network shows a decline of nitrate concentrations significantly lower than that of NOx emissions and ambient NOx concentrations. For sulfate, the decline lies between that of emissions and airborne concentrations of SO2. Back trajectory analysis and Potential Source Contribution Function mapping for 2014–2018 show that the highest concentrations of secondary constituents in southern England are associated with air masses originating in mainland Europe, with 42% of sulfate, 55% of nitrate, and 35% of SOC estimated to be associated with air masses entering the UK from the European mainland.

Impact of NOx and NH3 Emission Reduction on Particulate Matter across Po Valley: A LIFE-IP-PREPAIR Study

“…In addition, characteristic processes for the formation of particulate matter make the secondary fraction account for the great majority (more than 50%) of the total PM 2.5 concentrations, as shown by many studies [17][18][19][20][21][22]. Although other regions of Europe experience similar shares of secondary fractions of total PM (e.g., south of Poland [23], England [24,25], Greater Paris region [26] and other areas of France [27]), the Po Valley is a peculiar site where non-linear processes (i.e., the non-linear response of pollutant concentrations to an emission change) [28][29][30] and large variations in seasonal and spatial chemical regimes occur [31,32]. Still today, chemical regimes and secondary particle processes remain partly unknown; however, clear is the role of nitrogen oxides and ammonia as PM 2.5 precursors.…”