Examination of a tropospheric ozone control methodology from the explicit representation of POCPs across varying temporal and continent spatial domains

Abstract

Ozone is an internationally recognized criteria air pollutant, and remains a major concern despite more than 25 years of regulation at the national level. A method developed by Derwent and co- workers (1996, 1998) and initially applied in the United Kingdom (UK) , was to define POCPs (photochemical ozone creation potentials), as a means of ranking, in a semi-quantitative way, the contributions of different non-methane volatile organic compounds (VOCs) to ozone formation. To develop an understanding of the differences in high ozone formation in other regions of the world, subsequent modeling studies determined POCPs for the USA and Asia (The Pearl River Delta (PRD), China and Hong Kong (HK)), each region with different VOC and NOx emissions and characteristics. In this study POCP's are calculated on the Australian continent, for the city of Perth, of notably lower levels of air pollution than all previous studies. The POCP values were generally found to be lower than those determined previously in the UK, USA and Asia. An assessment is made of the similarities and differences between the four continents, first by VOC group classification and then by analyzing the ranking of the VOC in terms of the highest 50 POCP values from across all studies. Despite different geographic locations, meteorology and emissions (VOC and NOx), leading to differing temporal peak ozone duration and concentration at the receptors, a number key VOC were found to he high ozone contributors across all locations. This shows a dominance of alkene and aromatic compounds, and 25 of the 50 VOC with the highest POCP values are common across the region studied. These VOC are ethene, propene, isoprene, the butenes and pentenes, and though some of the aromatic compounds differed between the regions, the trimethyl benzenes were also consistently highly ranked. They are identified as key target VOC for consideration in emissions reduction strategies. Other VOC that influence ozone in specific regions were found to generally rank low in the highest 50 POCP groups, however the region specific ranking of formaldehyde, acetaldehyde and diethyl ether can be inferred as significant from their higher ranking positions in HK, Perth and the USA, should also be taken into consideration in targeted reductions. Given the commonality of the identified key VOC with the much more highly polluted airsheds also shows that the determination of POCP's for Perth has provided insightful intercomparisons, using the POCP ranking from across the regions, to identify key anthropogenic emitted VOC, that will most likely continue to be significant contributors to high ozone events in Perth, as the region experiences high population and development growth, with a significantly increasing burden on the regions VOC and NOx emissions. The study provides further support that the POCP methodology has considerable potential for application in policy development. The need for practical abatement policies is substantial with the growing need to redress the large increase in the occurrence of episodic high ozone concentrations in many rapidly developing regions of the world.