Developing receptor-oriented methods for non-methane hydrocarbon characterisation in urban air—Part I: source identification

The identification of non-methane hydrocarbons (NMHC) main sources is described at urban scale including their spatial and temporal variations. It is based on a receptor-oriented methodology derived from 4-year continuous and hourly measurements of nearly 40 C2–C9 ambient NMHC carried out at two urban sites of the medium-sized city of Lille, northern France. The methods devoted to sources identification included three complementary approaches: univariate statistics through the analysis of the ambient level time series, bivariate statistics through an original NMHC/acetylene Graphical Ratio Analysis which consisted in the study of the temporal evolution of the ambient level ratios and their comparison with those derived from vehicle exhaust emission factors, and multivariate statistics through various summertime and wintertime principal component analysis. Four main categories of sources were consistently identified: (1) motor vehicle exhaust, which dominates the NMHC distribution and particularly in winter, even for isoprene (2) wintertime stationary combustion and activities related to fossil fuel consumption in general (3) summertime evaporative emissions from fuel and solvent (4) summertime biogenic emissions for isoprene and their dependence on temperature and insolation.