Source determination of light non-methane hydrocarbons by simultaneous multi-site sampling in a metropolitan area

Abstract

Concentration profiles of C₂–C₆ non-methane hydrocarbons (NMHCs) were obtained in metropolitan Taipei, Taiwan based on 50 air samples collected simultaneously during an evening traffic rush hour. Although motor vehicle exhaust contributes most of the measured hydrocarbons in the city, levels of propane and butane are significant, and do not correlate well with typical NMHCs emitted from vehicle exhaust, suggesting that the leakage from liquefied petroleum gas (LPG) is the primary source. Natural gas (NG) leakage was also investigated using ethane as a tracer, and a similar profile to propane was observed, suggesting that the use of LPG and NG in metropolitan Taipei is not exclusive but rather complementary. The reactivity of ethane, propane, iso-and n-butanes released from NG and LPG was estimated to be about 5–6% of the total reactivity summed from C₂–C₆ NMHCs, compared to their mass fraction of about 27%. The profiles computed from simultaneous sampling provide a direct view of NMHC distributions in Taipei metropolitan area, and are useful to indicate source strength with respect to geographic locations. The principle component analysis, however, can reveal relative importance of various sources in a particular location or area.