Time trends of persistent organic pollutants (POPs) and Chemicals of Emerging Arctic Concern (CEAC) in Arctic air from 25 years of monitoring.

The long-term time trends of atmospheric pollutants at eight Arctic monitoring stations are reported. The work was conducted under the Arctic Monitoring and Assessment Programme (AMAP) of the Arctic Council. The monitoring stations were: Alert, Canada; Zeppelin, Svalbard; Stórhöfði, Iceland; Pallas, Finland; Andøya, Norway; Villum Research Station, Greenland; Tiksi and Amderma, Russia. Persistent organic pollutants (POPs) such as α- and γ-hexachlorocyclohexane (HCH), polychlorinated biphenyls (PCBs), α-endosulfan, chlordane, dichlorodiphenyltrichloroethane (DDT) and polybrominated diphenyl ethers (PBDEs) showed declining trends in air at all stations. However, hexachlorobenzene (HCB), one of the initial twelve POPs listed in the Stockholm Convention in 2004, showed either increasing or non-changing trends at the stations. Many POPs demonstrated seasonality but the patterns were not consistent among the chemicals and stations. Some chemicals showed winter minimum and summer maximum concentrations at one station but not another, and vice versa. The ratios of chlordane isomers and DDT species showed that they were aged residues. Time trends of perfluorooctanoic acid (PFOA) and perfluorooctane sulfonic acid (PFOS) were showing decreasing concentrations at Alert, Zeppelin and Andøya. The Chemicals of Emerging Arctic Concern (CEAC) were either showing stable or increasing trends. These include methoxychlor, perfluorohexane sulfonic acid (PFHxS), 6:2 fluorotelomer alcohol, and C9-C11 perfluorocarboxylic acids (PFCAs). We have demonstrated the importance of monitoring CEAC before they are being regulated because model calculations to predict their transport mechanisms and fate cannot be made due to the lack of emission inventories. We should maintain long-term monitoring programmes with consistent data quality in order to evaluate the effectiveness of chemical control efforts taken by countries worldwide.

Diurnal Variability and Emission Pattern of Decamethylcyclopentasiloxane (D5) from the Application of Personal Care Products in Two North American Cities.

Decamethylcyclopentasiloxane (D5) is a cyclic volatile methyl siloxane (cVMS) that is widely used in consumer products and commonly observed in urban air. This study quantifies the ambient mixing ratios of D5 from ground sites in two North American cities (Boulder, CO, USA, and Toronto, ON, CA). From these data, we estimate the diurnal emission profile of D5 in Boulder, CO. Ambient mixing ratios were consistent with those measured at other urban locations; however, the diurnal pattern exhibited similarities with those of traffic-related compounds such as benzene. Mobile measurements and vehicle experiments demonstrate that emissions of D5 from personal care products are coincident in time and place with emissions of benzene from motor vehicles. During peak commuter times, the D5/benzene ratio (w/w) is in excess of 0.3, suggesting that the mass emission rate of D5 from personal care product usage is comparable to that of benzene due to traffic. The diurnal emission pattern of D5 is estimated using the measured D5/benzene ratio and inventory estimates of benzene emission rates in Boulder. The hourly D5 emission rate is observed to peak between 6:00 and 7:00 AM and subsequently follow an exponential decay with a time constant of 9.2 h. This profile could be used by models to constrain temporal emission patterns of personal care products.

Nitryl chloride and molecular chlorine in the coastal marine boundary layer.

The magnitude and sources of chlorine atoms in marine air remain highly uncertain but have potentially important consequences for air quality in polluted coastal regions. We made continuous measurements of ambient ClNO(2) and Cl(2) concentrations from May 15 to June 8 aboard the Research Vessel Atlantis during the CalNex 2010 field study. In the Los Angeles region, ClNO(2) was more ubiquitous than Cl(2) during most nights of the study period. ClNO(2) and Cl(2) ranged from detection limits at midday to campaign maximum values at night reaching 2100 and 200 pptv, respectively. The maxima were observed in Santa Monica Bay when sampling the Los Angeles urban plume. Cl(2) at times appeared well correlated with ClNO(2), but at other times, there was little to no correlation implying distinct and varying sources. Well-confined Cl(2) plumes were observed, largely independent of ClNO(2), providing support for localized industrial emissions of reactive chlorine. Observations of ClNO(2), Cl(2), and HCl are used to constrain a simple box model that predicts their relative importance as chlorine atom sources in the polluted marine boundary layer. In contrast to the emphasis in previous studies, ClNO(2) and HCl are dominant primary chlorine atom sources for the Los Angeles basin.

Depression of ammonia uptake to sulfuric acid aerosols by competing uptake of ambient organic gases.

The neutralization of acidic aerosols by ammonia has been studied through experiments which combine ambient air with laboratory generated sulfuric acid aerosol. Results indicated that acidic aerosol mixed with organic free air and ammonia was neutralized on a time scale<1 min, consistent with expectations. However, in the presence of ambient organic gases and ammonia, the rate of aerosol neutralization is significantly reduced. This reduction in ammonia uptake was concurrent with an increase in the amount of particle phase organics. A steady state in the NH4+/SO4(2-) in the presence of organic gases was established on time scales of 10 min to several hours, corresponding to NH3 uptake coefficients in the range of 4×10(-3)-2×10(-4). The degree to which neutralization was slowed was dependent upon the initial ammonia concentration and the organic mass added to the aerosols. These results suggest that inorganic equilibrium thermodynamic models may overestimate the rate of ammonia uptake and that ambient particles may remain acidic for longer than previously expected.

Formation of volatile organic compounds in the heterogeneous oxidation of condensed-phase organic films by gas-phase OH.

The yield of volatile organic compounds (VOCs) from the heterogeneous oxidation of condensed-phase organic and hydrocarbon soot films by gas-phase OH has been studied in a coated-wall flow tube at room temperature. Simultaneously, OH concentrations are measured using a chemical-ionization mass spectrometer (CIMS) operated in negative ion mode and VOCs are measured using a commercial proton-transfer-reaction mass spectrometer (PTR-MS). It is observed that a variety of aldehydes/carbonyls and carboxylic acids are formed. Specifically, detailed experiments were conducted with stearic acid, where products are observed that contain as many as 13 carbon atoms with the average carbon number of the products between 3 and 5. The yield of VOCs, relative to the loss of OH radicals, is strongly dependent on the partial pressure of O2 in the carrier gas, ranging from 0.08 +/- 0.03 in a nominally pure He carrier gas to 0.34 +/- 0.14 in 6 Torr of pure O2. Yields from other organics are somewhat lower than those from stearic acid, ranging in conditions of pure O2 from 0.10 +/- 0.04 for BES (bis(ethylhexyl)sebacate), to 0.03 +/- 0.01 for n-hexane soot, to 0.01 +/- 0.005 for pyrene. Under atmospheric conditions, OH oxidation of select organics may be an efficient source of small VOCs. In particular, formic acid is formed in significant yield from all the surfaces.