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Atmospheric non-methane hydrocarbon compounds (NMHCs) were measured\udat a sampling site in Beijing city from 15 December 2015 to 14 January 2016\udto recognize their pollution levels, variation characteristics, and sources.\udWe quantified 53 NMHCs, and the proportions of alkanes, alkenes,\udacetylene, and aromatics to the total NMHCs were 49.8–55.8, 21.5–24.7,\ud13.5–15.9, and 9.3–10.7 %, respectively. The variation trends in the\udNMHC concentrations were basically identical and exhibited remarkable\udfluctuation, which was mainly ascribed to the variation in meteorological\udconditions, especially wind speed. The diurnal variations in NMHCs on clear\uddays exhibited two peaks during the morning and evening rush hours, whereas\udthe rush hours' peaks diminished or even disappeared on the haze days,\udimplying that the relative contribution of the vehicular emissions to\udatmospheric NMHCs depended on the pollution status. Two evident peaks of the\udpropane ∕ propene ratios appeared in the early morning before sun\udrise and at noontime on clear days, whereas only one peak occurred in the\udafternoon during the haze days, which were attributed to the relatively fast\udreactions of propene with OH, NO3, and O3. Based on the chemical\udkinetic equations, the daytime OH concentrations were calculated to be in the\udrange of 3. 47 × 105–1. 04 × 106 molecules cm−3 on\udclear days and 6. 42 × 105–2. 35 × 106 molecules cm−3 on haze days. The nighttime NO3\udconcentrations were calculated to be in the range of 2. 82 × 109–4. 86 × 109 molecules cm−3 on clear days. The\udcorrelation coefficients of typical hydrocarbon pairs (benzene ∕ toluene,\udo-xylene ∕ m,p-xylene, isopentane ∕ n-pentane, etc.) revealed that vehicular\udemissions and coal combustion were important sources for atmospheric NMHCs in\udBeijing during the wintertime. Five major emission sources for atmospheric\udNMHCs in Beijing during the wintertime were further identified by positive\udmatrix factorization (PMF), including gasoline-related emissions (gasoline\udexhaust and evaporation), coal combustion, diesel exhaust, acetylene-related\udemissions, and consumer and household products. Coal combustion (probably\uddomestic coal combustion) was found to make the greatest contribution\ud(29.6–33.4 %) to atmospheric NMHCs during haze days

The levels, variation characteristics, and sources of atmospheric non-methane hydrocarbon compounds during wintertime in Beijing, China