Long-term measurements (2009–2015) of non-methane hydrocarbons (NMHCs) in a megacity of China: implication for emission validation and source control
Abstract. Long term measurements of air pollutants represented the footprints of emissions to some extent, which could provide useful and consecutive evolution of emissions. Both atmospheric concentrations and emissions of many air pollutants have been reported decreasing in the past decade due to the implement of various control measures in China, which were different for non-methane hydrocarbons (NMHCs) with increasing emissions as reported previously. The present study employed the long-term (2009–2015) NMHCs measurements as well as the related social and economic activities data in Shanghai, a megacity in eastern China, to explore the evolution of NMHCs emissions during the periods. The meteorology and photochemistry which might impact the NMHCs measurements were tested as negligible effects on an annual scale. As a result, NMHCs mixing ratio showed no statistic interannual changes, of which compositions varied significantly. This resulted a statistically decreasing trend of ozone formation potential by 3.8 % yr−1 (p < 0.05, the same below), which should benefit to ozone pollution mitigation as its formation in VOC-control region in Shanghai. Observed alkanes, aromatics and acetylene increased/decreased by +3.8 % yr−1, −6.0 % yr−1 and −7.8 % yr−1 (p < 0.05), respectively, whereas alkenes showed no apparent trend. NMHCs sources were apportioned by the positive matrix factorization (PMF) model. Accordingly, vehicular emissions (−6.5 % yr−1) and petrochemical industry (−9.4 % yr−1) presented a significant decreasing trend, but the decrease slowed down in recent years; some positive reductions in solvent usage (−8.0 % yr−1) appeared after 2010; however, emissions of natural gas (+9.2 % yr−1) and fuel evaporation (with an increasing fraction) became more important. Discrepancies between measurements and emission inventory, both in interannual trend and speciation as well as source contributions, emphasized the need for further validation in NMHCs emission inventory in future. Our study confirmed the effectiveness of strengthening emission standards of vehicles and key industrial sources, generally mobile and point sources, against the increasing vehicle populations and industries in the past. While, limited reductions were observed for the fugitive emissions like petrochemical industry which need more effective measures in future. Emissions of natural gas and fuel evaporation deserved more attention as the quick increase of natural gas and fuel consumption due to the policy of energy structure reformation in China.
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