<p><strong>Abstract.</strong> Oil sands (OS) operations in Alberta, Canada are a large source of secondary organic aerosol (SOA). However, the SOA formation process from OS-related precursors remains poorly understood. In this work, a newly developed oxidation flow reactor (OFR), the Environment and Climate Change Canada OFR (ECCC-OFR), was characterized and used to study the yields and composition of SOA formed from OH oxidation of α-pinene, selected alkanes, and the vapors evolved from five OS-related samples (OS ore, naphtha, tailings pond water, bitumen, and dilbit). The derived SOA yields from α-pinene and selected alkanes using the ECCC-OFR were in good agreement with those of traditional smog chamber experiments, but significantly higher than those of other OFR studies under similar conditions. The results also suggest that gas-phase reactions leading to fragmentation (i.e., C-C bond cleavage) have a relatively small impact on the SOA yields in the ECCC-OFR at high photochemical ages, in contrast to other previously reported OFR results. Translating the impact of fragmentation reactions in the ECCC-OFR to ambient atmospheric conditions reduces its impact on SOA formation even further. These results highlight the importance of careful evaluation of OFR data, particularly when using such data to provide empirical factors for the fragmentation process in models. Application of the ECCC-OFR to OS-related precursor mixtures, demonstrated that the SOA yields from OS ore and bitumen vapors (maximum of ~ 0.6–0.7) are significantly higher than those from the vapors from solvent use (naphtha), effluent from OS processing (tailing pond water) and from the solvent diluted bitumen (dilbit) (maximum of ~ 0.2–0.3), likely due to the volatility of each precursor mixture. A comparison of the yields and elemental ratios (H / C and O / C) of the SOA from the OS-related precursors to those of linear and cyclic alkane precursors of similar carbon numbers suggests that cyclic alkanes play an important role in the SOA formation in the OS. The analysis further indicates that the majority of the SOA formed downwind of OS facilities is derived from open-pit mining operations (i.e., OS ore evaporative emissions), rather than from higher volatility precursors from solvent use during processing and/or tailing management. The current results have implications for improving the regional modeling of SOA from OS sources, for the potential mitigation of OS precursor emissions responsible for observed SOA downwind of OS operations, and for the understanding of petrochemical and alkane derived SOA in general.</p>

Abstract. Cyclic volatile methyl siloxanes (cVMSs), which can volatilize into the atmosphere, are active ingredients in widely used consumer products, thus attracting much attention due to their potential environmental risks. While in the atmosphere the cVMSs undergo oxidation, yielding both gaseous and particulate products. The aerosol yields and compositions from the OH oxidation of four cVMSs (D3–D6) were determined under low- and high-NOx conditions in an oxidation flow reactor. The aerosol yields increased progressively from D3 to D6, consistent with the volatilities and molecule weights of these cVMSs. NOx can restrict the formation of secondary organic aerosols (SOAs), leading to lower SOA yields under high-NOx conditions than under low-NOx conditions, with a yield decrease between 0.05–0.30 depending on the cVMSs. Ammonium sulfate seeds exhibited minor impacts on SOA yields under low-NOx conditions but significantly increased the SOA yields in the oxidation of D3–D5 at short photochemical ages under high-NOx conditions. The mass spectra of the SOAs showed a dependence of its chemical compositions on OH exposure. At high exposures equivalent to photochemical ages of >4 d in the atmosphere, D4–D6 SOAs mainly consisted of CxHy and CxHyOzSin under low-NOx conditions, whereas they primarily contained NmOz, CxHy, CxHyO1, CxHyO>1 and CxHyOzSin under high-NOx conditions. The potential contributions of cVMSs to SOA formation in the atmosphere were evaluated using the reported cVMSs annual production and the yield obtained in the present study. A global cVMS-derived (D4–D6) SOA source strength is estimated to be 0.01 Tg yr−1, distributed over major urban centers.

Abstract. Environmental temperature plays a vital role in controlling chemical transformations that lead to the formation of secondary organic aerosol (SOA), and ultimately impact composition and optical properties of the aerosol particles. In this study, we investigate optical properties of n-dodecane secondary organic aerosol under two temperature conditions: 5 °C and 25 °C. It is shown that low temperature can enhance the real part of refractive index (RI) of the SOA at the wavelengths of 532 nm and 375 nm. Mass spectrometry analysis reveals that molecular composition of n-dodecane SOA is significantly modified by temperature: a large amount of oligomers are formed under low temperature condition, which lead to higher RI values. These findings will help improve our understanding of the chemical composition and optical properties of SOA under different temperature conditions, and provide another possible explanation of the low visibility during winter.

<p><strong>Abstract.</strong> Measurements of volatile organic compounds (VOCs) were performed at a suburban site and an urban site in Beijing during the winter of 2014–2015. The VOC concentrations and emission ratios (ERs) to CO were compared at these two sites. It is found that though the VOC concentrations at the urban site are 2.67 ± 1.15 times of those at the suburban site, the ERs are similar (within a factor of 1.5). It is indicated that: (1) the VOCs at suburban areas are mainly from the transportation from the urban areas; (2) the ERs measured at the urban areas are also valid for the surrounding suburban areas. By comparing the diurnal variations and the contribution of anthropogenic emissions at both sites, we find that the photochemical processes are very active at the urban site, and these processes play an important role in the daytime oxygenated VOCs (OVOCs) formation. The methanol at the urban site and the formic acid at the suburban site probably have additional sources, which are attributed to be solvent use and soil/agriculture, respectively. The festival effects from Chinese New Year (CNY) were investigated. The VOC concentrations decreased ~ 60 % during CNY holidays, probably due to the population migration during festival holidays. In addition, fireworks are found to be an important source of acetonitrile, aromatics, and some OVOCs during CNY festival, and should be controlled more strictly. This study provides key characteristics of wintertime VOCs in suburban and urban Beijing, and has implications for better understanding the atmospheric chemistry of VOCs in and around this megacity.</p>