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Abstract: Black carbon (BC) or soot particles formed by combustion are ubiquitous in the atmosphere and have a significant effect on climate and human health. Oxidation can change the physicochemical characteristics of BC, thereby increasing its toxicity. The physicochemical properties of BC and ozone-oxidized BC are investigated in this study through transmission electron microscopy, X-ray photoelectron spectroscopy, diffuse reflectance infrared Fourier transform spectroscopy, ultraviolet–visible spectrophotometry, and electron paramagnetic resonance. The contents of oxygen-containing functional groups, hydrophilicity, water-soluble organic compounds, and free radicals increased after ozone treatment. The redox capacity and cytotoxicity of BC particles were enhanced by ozone oxidation as detected by dithiothreitol (DTT) and 3-(4,5-Dimethylthiazol-2-yl)-2,5-diphenyltetrazoliumbromide assays. The redox activities of different BC particles are compared. Particle phase contributed significantly to total redox activity as detected by the DTT assay. Results indicate that BC particles that have undergone aging in the atmosphere may be more toxic and harmful to human health. [ABSTRACT FROM AUTHOR]

Abstract: Formaldehyde is one of the most important carbonyl organic compounds. Heterogeneous reactions of formaldehyde on the surface of oxides of crustal elements could be an important sink for formaldehyde in the atmosphere. In this study, the kinetics of the heterogeneous reaction of formaldehyde on the surface of γ-Al2O3 was investigated in situ by diffuse reflectance infrared Fourier-transform spectroscopy (DRIFTS) combined with ion chromatography (IC), X-ray diffraction (XRD), and field emission environmental scanning electron microscope (ESEM). The adsorbed species, formate, dioxymethylene, polyoxymethylene, and formaldehyde, on γ-Al2O3 particles, were identified by infrared spectroscopy. On the surface of γ-Al2O3 particles, formaldehyde is first oxidized to dioxymethylene, which is further oxidized to formate. The reaction order was determined as 0.74 ± 0.05, and the initial reactive uptake coefficients at room temperature were calculated with the geometric and Brunauer–Emmett–Teller specific surface areas as (3.6 ± 0.8) × 10−4 and (1.4 ± 0.31) × 10−8, respectively. The influences of oxygen concentration, humidity, and temperature on the reaction products and reactive uptake coefficients were studied. The results indicated the reaction is independent of the O2 concentration within the range used in this experiment, and humidity is negatively correlated with the uptake of formaldehyde by the particles. Temperature not only plays a role on the heterogeneous reaction products but also is positively correlated with the uptake rate of formaldehyde by γ-Al2O3 particles in the troposphere. The apparent activation energy of the reaction was determined. [Copyright &y& Elsevier]

A field observation focusing on reactive oxygen species (ROS) was conducted before, during, and after the 2015 China Victory Day Parade to understand the influence of short-term emissions controls on atmospheric oxidative activity. The hourly average concentrations of PM 2.5 , SO 2 , NO, NO 2 , CO, O 3 , as well as gas and particle-phase ROS, were measured using a series of online instruments. PM 2.5 concentrations during control days were significantly lower than non-control days, which directly lead to the “Parade Blue”, yet reductions of most gaseous pollutants except SO 2 were not so obvious as PM. Similarly, the control measures also led to a great loss of particle-phase ROS throughout the control period, while the reduction of ROS in gas phase was not obvious until the more stringent measures implemented since September 1. Furthermore, only weak positive correlations were observed among ROS and some other measured species, indicating ROS concentrations were affected by a number of comprehensive factors that single marker could not capture. Meanwhile, meteorological condition and regional transportation were also shown to be the minor factors affecting atmospheric oxidizing capacity. The results of this observation mainly revealed the control measures were conducive to reducing particle-related ROS. However, the reduction of gas-phase ROS activity was less effective given the menu of controls employed for the 2015 China Victory Day Parade. Therefore, short-term emissions controls only aimed to PM reduction and visibility improvement will produce the blue sky but will not equivalently reduce the gas-phase ROS. Supplemental control measures will be needed to further reduce gas-phase ROS concentrations. [ABSTRACT FROM AUTHOR]

The contributions of soluble and insoluble fractions of soot particles, as well as their ozonised products, to oxidative potential (OP), warrant investigation. In our study, soot particles generated under two air/fuel ratio (A/F) conditions were aged by ozone (O 3) at an atmospherically relevant level in a chamber. The OP values of total soot particles and the methanol- and water-soluble fractions were measured by the dithiothreitol (DTT) assay (OPDTT). Results showed that both A/F and O 3 aging influenced the OPDTT of different fractions. Lower A/F favoured increases in OPDTT for both total soot and its soluble fractions. The highest OPDTT increments after O 3 aging were found in the methanol-soluble fraction of high-A/F soot and the insoluble fraction of low-A/F soot. Phenanthrene (PHE), one of the dominant polycyclic aromatic hydrocarbons (PAHs) in soot particles, was selected as a model PAH to investigate O 3 -PAH aging using in situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS), with phenanthrenequinone (PQ) and 1,1′-biphenyl-2,2′-dicarboxaldehyde (BD) identified as two major ozonised products. Furthermore, the quantitative contributions of PQ and BD to the OPDTT increases in ozonised soot were extrapolated. In particular, for ozonised low-A/F soot, PQ alone contributed 12.5% to the OPDTT increase. This work highlights the vital contributions of PQ and other key ozonised products of PAHs adsorbed on soot surfaces to the enhanced OPDTT values and potential toxicity of aged soot, which enhances current understanding regarding the health effects of aged soot in the atmosphere. Image 1 • Both A/F and O 3 aging influenced the OPDTT of different soot fractions. • Methanol-soluble organics were the dominant contributors to the total OPDTT. • A/F also affected the sensitivity of different fractions of soot to O 3. • PQ and BD production accounted for 41% and 16% of PHE consumption in O 3 aging. • PQ formation significantly contributed to the OPDTT increases in ozonised soot. [ABSTRACT FROM AUTHOR]

Solar irradiation plays a key role in promoting nitrous acid (HONO) production from surface enhanced photochemical reactions such as photolysis of nitrate. Nitrate anions are ubiquitous in ambient particles and on various outdoor and indoor surfaces, with reported surface density from 10−7 to 10−3 mol m−2. In this work, we measured HONO and NO 2 production from surface nitrate photolysis under eight narrow bandwidth light sources with peak emission wavelengths ranging from 300 to 605 nm. We defined the probability of HONO and NO 2 release per surface nitrate absorbing unit photon density of particular wavelength as "reactive cross section" of surface nitrate. Relative to the absorption cross section of gaseous HNO 3 , the reactive cross section of surface nitrate was found enhanced by up to 970-fold. The reactive cross section determined in our laboratory decreased from (6.3 ± 0.5) × 10−20 cm2 molecule−1 at 300 nm to (1.0 ± 0.3) × 10−24 cm2 molecule−1 at 605 nm, and showed a nonlinear relationship with the surface density of nitrate. Outdoor HONO production was mostly attributed to solar UV irradiation as expected, while underappreciated indoor HONO accumulation was also feasible considering HONO production induced by visible light and large specific surface area indoors. We then constructed a dynamic model to further evaluate the indoor HONO source in typical indoor environments. Photochemical properties of this HONO source lead to diurnal profiles in indoor HONO accumulation, with daily average HONO accumulation ranging from 1.1 to 17.8 ppb under various conditions. The model calculation confirmed that visible light substantially promotes surface nitrate photolysis and indoor HONO accumulation, with an average daily strength that is 0.28–0.34 mg h−1 at surface nitrate of 10−4 mol m−2 under simulated sunlight illumination. Our results call for direct measurements of indoor HONO in a variety of real indoor environments. [Display omitted] • Enhanced reactive cross section of surface nitrate from 300 to 605 nm was obtained. • Daily average HONO accumulation ranges from 1.1 to 17.8 ppb under various conditions. • HONO source strength induced by visible light is simulated to be 0.28–0.34 mg h−1. [ABSTRACT FROM AUTHOR]