ALBERT

Description: Water-soluble organic compounds (WSOCs) are important components of organics in the atmospheric fine particulate matter. Although WSOCs play an important role in the hygroscopicity of aerosols, knowledge on the water uptake behavior of internally mixed WSOC aerosols remains limited. Here, the hygroscopic properties of single components such as levoglucosan, oxalic acid, malonic acid, succinic acid, phthalic acid, and multicomponent WSOC aerosols mainly involving oxalic acid are investigated with the hygroscopicity tandem differential mobility analyzer (HTDMA). The coexisting hygroscopic species including levoglucosan, malonic acid, and phthalic acid have a strong influence on the hygroscopic growth and phase behavior of oxalic acid, even suppressing its crystallization completely during the drying process. The phase behaviors of oxalic acid/levoglucosan mixed particles are confirmed by infrared spectra. The discrepancies between measured growth factors and predictions from Extended Aerosol Inorganics Model (E-AIM) with the Universal Quasi-Chemical Functional Group Activity Coefficient (UNIFAC) method and Zdanovskii–Stokes–Robinson (ZSR) approach increase at medium and high relative humidity (RH) assuming oxalic acid in a crystalline solid state. For the internal mixture of oxalic acid with levoglucosan or succinic acid, there is enhanced water uptake at high RH compared to the model predictions based on reasonable oxalic acid phase assumption. Organic mixture has more complex effects on the hygroscopicity of ammonium sulfate than single species. Although hygroscopic species such as levoglucosan account for a small fraction in the multicomponent aerosols, they may still strongly influence the hygroscopic behavior of ammonium sulfate by changing the phase state of oxalic acid which plays the role of "intermediate" species. Considering the abundance of oxalic acid in the atmospheric aerosols, its mixtures with hygroscopic species may significantly promote water uptake under high RH conditions and thus affect the cloud condensation nuclei (CCN) activity, optical properties, and chemical reactivity of atmospheric particles.

Description: 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 (tailings 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 tailings 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.

Description: In this work, the heterogeneous reactions of NO2 with CaCO3-(NH4)2SO4 mixtures with a series of weight percentage (wt%) of (NH4)2SO4 were investigated using a diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) at different relative humidity (RH) values. For comparison, the heterogeneous reactions of NO2 with pure CaCO3 particles and pure (NH4)2SO4 particles, as well as the reaction of CaCO3 with (NH4)2SO4 particles were also studied. The results indicated that NO2 did not show any significant uptake on pure (NH4)2SO4 particles, and it reacted with pure CaCO3 particles to form calcium nitrate at all the RHs investigated. The heterogeneous reactions of NO2 with CaCO3-(NH4)2SO4 mixtures were markedly dependent on RH. Calcium nitrate was formed from the heterogeneous reactions of NO2 with the mixtures under both dry and wet conditions, whereas CaSO4·0.5H2O (bassanite), CaSO4·2H2O (gypsum) and (NH4)2Ca(SO4)2·H2O (koktaite) were produced depending on RH. The NO3− mass concentrations of the CaCO3-(NH4)2SO4 mixtures had a negative linear relation with (NH4)2SO4 mass fraction under dry condition. In this condition, the heterogeneous uptake of NO2 on the mixtures was similar to that on pure CaCO3 particles. The CaCO3-(NH4)2SO4 mixtures exhibited a promotive effect on the heterogeneous uptake of NO2 and the formation of nitrate under wet conditions. Additionally, the reaction between CaCO3 and (NH4)2SO4 was enhanced with increasing RH, and it exhibited an inhibiting effect on the formation of nitrate. On the contrary, the interaction between Ca(NO3)2 and (NH4)2SO4 promoted the nitrate formation during the heterogeneous reaction process. Furthermore, the heterogeneous uptake of NO2 on CaCO3-(NH4)2SO4 mixtures was found to favor the formation of bassanite and gypsum due to the decomposition of CaCO3 and the coagulation of Ca2+ and SO42−. A possible reaction mechanism was proposed and atmospheric implications were discussed.

Description: 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.

Description: In this work, the heterogeneous reactions of NO2 with CaCO3–(NH4)2SO4 mixtures with a series of weight percentage (wt %) of (NH4)2SO4 were investigated using diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) at different relative humidity (RH) values. For comparison, the heterogeneous reactions of NO2 with pure CaCO3 particles and pure (NH4)2SO4 particles, as well as the reaction of CaCO3 with (NH4)2SO4 particles, were also studied. The results indicated that NO2 did not show any significant uptake on (NH4)2SO4 particles, and it reacted with CaCO3 particles to form calcium nitrate under both dry and wet conditions. The heterogeneous reactions of NO2 with CaCO3–(NH4)2SO4 mixtures were markedly dependent on RH. Calcium nitrate was formed from the heterogeneous reactions at all the RHs investigated, whereas CaSO4  ⋅  0.5H2O (bassanite), CaSO4  ⋅  2H2O (gypsum), and (NH4)2Ca(SO4)2  ⋅  H2O (koktaite) were produced depending on RH. Under the dry condition, the heterogeneous uptake of NO2 on the mixtures was similar to that on CaCO3 particles with neglectable effects from (NH4)2SO4; the duration of initial stages and the NO3− mass concentrations had a negative linear relation with the mass fraction of (NH4)2SO4 in the mixtures. Under wet conditions, the chemical interaction of (NH4)2SO4 with Ca(NO3)2 enhances the nitrate formation, especially at medium RHs, while the coagulation of (NH4)2SO4 with CaCO3 exhibits an increasing inhibiting effects with increasing RH at the same time. In addition, the heterogeneous uptake of NO2 on the mixtures of CaCO3 and (NH4)2SO4 was found to favor the formation of bassanite and gypsum due to the decomposition of CaCO3 and the coagulation of Ca2+ and SO42−. A possible reaction mechanism was proposed and the atmospheric implications were discussed.