Decadal Trends of Speciated Non-methane Hydrocarbons in Taipei

Selected non-methane hydrocarbons (NMHCs) obtained from long-term operation of the Photochemical Assessment Monitoring Stations (PAMS) in Taipei allowed for the assessment of the effectiveness of emission control measures on ozone precursors from 2007 to 2016. Despite the very pronounced diurnal and seasonal cycles of all the 51 target compounds, almost all species showed various degrees of declining trends over the decade. When dividing the 51 compounds into five groups of alkanes, alkenes, ethyne, aromatics, and isoprene, the decadal trends are assessed as −0.7 ± 0.8, −0.3 ± 0.1, −0.02 ± 0.14, −1.9 ± 1.2, and − 0.09 ± 0.02 ppbC year⁻¹, respectively. Meanwhile, as evidenced by multiple NMHC ratios as effective indicators of atmospheric photochemical conditions, a trend of gradual lessening in the degree of photochemistry over time was noticed. Air masses in Taipei are suggested to be increasingly more contributed by local emissions and less affected by mixing with transboundary or long-range transported influences.