Abstract. Atmospheric non-methane hydrocarbon compounds (NMHCs) were measured at a sampling site in Beijing city from 15 December 2015 to 14 January 2016 to recognize their pollution levels, variation characteristics and sources. Fifty-three NMHCs were quantified and the proportions of alkanes, alkenes, acetylene and aromatics to the total NMHCs were 49.8 % ~ 55.8 %, 21.5 % ~ 24.7 %, 13.5 % ~ 15.9 % and 9.3 % ~ 10.7 %, respectively. The variation trends of the NMHCs concentrations were basically identical and exhibited remarkable fluctuation, which were mainly ascribed to the variation of meteorological conditions, especially wind speed. The diurnal variations of NMHCs in clear days exhibited two peaks during the morning and evening rush hours, whereas the rush hours' peaks diminished or even disappeared in the haze days, implying that the relative contribution of the vehicular emission to atmospheric NMHCs depended on the pollution status. Two evident peaks of the propane/propene ratios respectively appeared in the early morning before sun rise and at noontime in clear days, whereas only one peak occurred in the afternoon during the haze days, which were attributed to the relatively fast reactions of propene with OH, NO3 and O3. Based on the chemical kinetic equations, the daytime OH concentrations were calculated to be in the range of 3.47 × 105–1.04 × 106 molecules cm−3 in clear days and 6.42 × 105–2.35 × 106 molecules cm−3 in haze days, and the nighttime NO3 concentrations were calculated to be in the range of 2.82 × 109–4.86 × 109 molecules cm−3 in clear days. The correlation coefficients of typical hydrocarbons pairs (benzene/toluene, o-xylene/m,p-xylene, isopentane/n-pentane, etc.) revealed that vehicular emission and coal combustion were important sources for atmospheric NMHCs in Beijing during the wintertime. Five major emission sources for atmospheric NMHCs in Beijing during the wintertime were further identified by positive matrix factorization (PMF), including vehicular emission and gasoline evaporation, coal combustion, solvent usage, acetylene-related emission and consumer and household products. Coal combustion (probably domestic coal combustion) were found to make the greatest contribution (29.4 ~ 33.4 %) to atmospheric NMHCs during haze days.
The H-theorem for the chemical kinetic equations with discrete time and for their generalizations