Long term trends of methane, non methane hydrocarbons, and carbon monoxide in urban atmosphere

Abstract

The concentrations of methane (CH4), non-methane hydrocarbons (NMHC), and carbon monoxide (CO) were measured at two urban locations (Guro (GR) and Nowon (NW)) in Seoul, Korea between 2004 and 2013. The mean amount fractions of CH4, NMHC, and CO, measured at GR over this period were 2.06 +/- 0.02, 0.32 +/- 0.03, and 0.61 +/- 0.05 ppm, respectively, while atNWtheywere 2.08 +/- 0.06, 0.33 +/- 0.05, and 0.54 +/- 0.06 ppm, respectively. The ratio of CH4 to the total hydrocarbon amount fraction remained constant across the study years: 0.82 to 0.90 at GR and 0.81 to 0.89 at NW. Similarly, stable ratios were also observed between NMHC and THC at the two sites. In contrast, the annual mean ratios for CH4/NMHC showed a larger variation: between 4.55 to 8.67 at GR and 4.25 to 8.45 at NW. The seasonality of CO was characterized by wintertime maxima, while for CH4 and NMHC the highest amount fractions were found in fall. The analysis of their long-term trends based on Mann-Kendall and Sen'smethods showed an overall increase of THC and CH4, whereas a decreasing trendwas observed for NMHC and CO. (C) 2015 Elsevier B.V. All rights reserved.