The recent decline in sea ice cover in the Arctic Ocean could affect the regional radiative forcing via changes in sea ice-atmosphere exchange of dimethyl sulfide (DMS) and biogenic aerosols formed from its atmospheric oxidation, such as methanesulfonic acid (MSA). This study examines relationships between changes in total sea ice extent north of 70 degrees N and atmospheric MSA measurement at Alert, Nunavut, during 1980-2009; at Barrow, Alaska, during 1997-2008; and at Ny-Alesund, Svalbard, for 1991-2004. During the 1980-1989 and 1990-1997 periods, summer (July-August) and June MSA concentrations at Alert decreased. In general, MSA concentrations increased at all locations since 2000 with respect to 1990 values, specifically during June and summer at Alert and in summer at Barrow and Ny-Alesund. Our results show variability in MSA at all sites is related to changes in the source strengths of DMS, possibly linked to changes in sea ice extent as well as to changes in atmospheric transport patterns. Since 2000, a late spring increase in atmospheric MSA at the three sites coincides with the northward migration of the marginal ice edge zone where high DMS emissions from ocean to atmosphere have previously been reported. Significant negative correlations are found between sea ice extent and MSA concentrations at the three sites during the spring and June. These results suggest that a decrease in seasonal ice cover influencing other mechanisms of DMS production could lead to higher atmospheric MSA concentrations.

Reliable characterization of particles freshly emitted from the ocean surface requires a sampling method that is able to isolate those particles and prevent them from interacting with ambient gases and particles. Here we report measurements of particles directly emitted from the ocean using a newly developed in situ particle generator (Sea Sweep). The Sea Sweep was deployed alongside R/V Atlantis off the coast of California during May of 2010. Bubbles were generated 0.75 m below the ocean surface with stainless steel frits and swept into a hood/vacuum hose to feed a suite of aerosol instrumentation on board the ship. The number size distribution of the directly emitted, nascent particles had a dominant mode at 55-60 nm (dry diameter) and secondary modes at 30-40 nm and 200-300 nm. The nascent aerosol was not volatile at 230 degrees C and was not enriched in SO4=, Ca++, K+, or Mg++ above that found in surface seawater. The organic component of the nascent aerosol (7% of the dry submicrometer mass) volatilized at a temperature between 230 and 600 degrees C. The submicrometer organic aerosol characterized by mass spectrometry was dominated by non-oxygenated hydrocarbons. The nascent aerosol at 50, 100, and 145 nm dry diameter behaved hygroscopically like an internal mixture of sea salt with a small organic component. The CCN/CN activation ratio for 60 nm Sea Sweep particles was near 1 for all supersaturations of 0.3 and higher indicating that all of the particles took up water and grew to cloud drop size. The nascent organic aerosol mass fraction did not increase in regions of higher surface seawater chlorophyll but did show a positive correlation with seawater dimethylsulfide (DMS).

In this work, a closure experiment for tropospheric aerosol is presented. Aerosol size distributions and single scattering albedo from remote sensing data are compared to those measured in-situ. An aerosol pollution event on 4 April 2009 was observed by ground based and airborne lidar and photometer in and around Ny-Alesund, Spitsbergen, as well as by DMPS, nephelometer and particle soot absorption photometer at the nearby Zeppelin Mountain Research Station. The presented measurements were conducted in an area of 40 x 20 km around Ny-Alesund as part of the 2009 Polar Airborne Measurements and Arctic Regional Climate Model Simulation Project (PAMARCMiP). Aerosol mainly in the accumulation mode was found in the lower troposphere, however, enhanced backscattering was observed up to the tropopause altitude. A comparison of meteorological data available at different locations reveals a stable multi-layer-structure of the lower troposphere. It is followed by the retrieval of optical and microphysical aerosol parameters. Extinction values have been derived using two different methods, and it was found that extinction (especially in the UV) derived from Raman lidar data significantly surpasses the extinction derived from photometer AOD profiles. Airborne lidar data shows volume depolarization values to be less than 2.5% between 500 m and 2.5 km altitude, hence, particles in this range can be assumed to be of spherical shape. In-situ particle number concentrations measured at the Zeppelin Mountain Research Station at 474 m altitude peak at about 0.18 mu m diameter, which was also found for the microphysical inversion calculations performed at 850 m and 1500 m altitude. Number concentrations depend on the assumed extinction values, and slightly decrease with altitude as well as the effective particle diameter. A low imaginary part in the derived refractive index suggests weakly absorbing aerosols, which is confirmed by low black carbon concentrations, measured at the Zeppelin Mountain as well as on board the Polar 5 aircraft. (C) 2011 Elsevier Ltd. All rights reserved.

Gaseous and size-segregated particulate PBDEs (specifically BDE-47, -99, -183, -207, and -209) in the air were measured in urban Guangzhou at 100 and 150 m above the ground in daytime and at night in August and December 2010, to assess dry deposition of these contaminants accurately with regards to influences of meteorological factors but without confounding surface effects. Particulate PBDEs were more abundant at night than in daytime, and slightly higher in winter than in summer, likely from varying meteorological conditions and atmospheric boundary layers. More than 60% of particulate-phase PBDEs was contained in particles with an aerodynamic diameter (D-P) below 1.8 mu m, indicating long-range transport potential. The average daily particle dry deposition fluxes of PBDEs in August ranged from 2.6 (BDE-47) to 88.6 (BDE-209) ng m(-2) d(-1), while those in winter ranged from 2.0 (BDE-47) to 122 (BDE-209) ng m(-2) d(-1). Deposition fluxes of all PBDE congeners were significantly higher in daytime than at night for both months, due to the effect of diurnal variability of meteorological factors. In addition, mean overall particle deposition velocities of individual BDE congeners ranged from 0.11 to 0.28 cm s(-1). These values were within a factor of 2 of assumed values previously used in southern China and the Laurentian Great Lakes, suggesting that such assumptions were reasonable for sites with similar particulate size distributions and PBDE sources. Dry deposition velocities of PBDEs were lower at night than those in the daytime, probably reflecting higher mechanical and thermal turbulence during daytime. Dry deposition of particulate-bound PBDEs is influenced by short-term temporal variability from meteorological factors, and also by particulate size fractions.

Atmospheric black carbon (BC) warms Earth's climate, and its reduction has been targeted for near-term climate change mitigation. Models that include forcing by BC assume internal mixing with non-BC aerosol components that enhance BC absorption, often by a factor of similar to 2; such model estimates have yet to be clearly validated through atmospheric observations. Here, direct in situ measurements of BC absorption enhancements (E-abs) and mixing state are reported for two California regions. The observed E-abs is small-6% on average at 532 nm-and increases weakly with photochemical aging. The E-abs is less than predicted from observationally constrained theoretical calculations, suggesting that many climate models may overestimate warming by BC. These ambient observations stand in contrast to laboratory measurements that show substantial E-abs for BC are possible.

Polycyclic aromatic hydrocarbons (PAHs) associated with inhalable particles are harmful to human health, especially to people in urban indoor environments. To evaluate human respiratory exposure to indoor PAHs properly, respiratory deposition fluxes of size-fractioned PAHs were estimated based on size-segregated distribution of PAHs in indoor air of an urban community of Guangzhou, China. The concentrations of Sigma(16)PAH (sum of the 16 priority PAHs designated by the United States Environmental Protection Agency) were 28.9 +/- 10.0 ng/m(3), with the mean benzo(a)pyrene equivalent (BaPE) concentration at 4.1 +/- 1.6 ng/m(3). Particle size distributions of both Sigma(16)PAH and BaPE concentrations peaked in the 1.0-1.8 mu m fraction. The mean respiratory deposition flux of Sigma(16)PAH was 5.9 ng/h, and accumulation mode particles contributed 20.5-83.8% of the respiratory deposition fluxes for individual PAHs. In addition, 8.6-10.2% of inhaled Sigma(16)PAH were calculated to be deposited in the alveoli region, with accumulation particles as the largest contributor. In particular, ultrafine particles contributed 0.4-21.7% of individual PAHs deposited in the alveoli region, more than twice the fraction of the PAHs in the ultrafine particles (0.2-8.5%). Finally, lifetime cancer risk via inhalation of indoor particulate PAHs may be greater than the cancer risk guideline value (10(-6)). depending on specific assumptions used in this risk assessment. (C) 2012 Elsevier B.V. All rights reserved.

The Arctic is undergoing rapid environmental change, manifested most dramatically by reductions in sea ice extent and thickness. The changes are attributed to anthropogenic effects related to greenhouse warming, with secondary contributions from changing ocean and wind currents as well as from pollutants, especially “absorbing” black carbon. The warmer Arctic air temperatures and new patterns of wind and ocean circulation have also contributed to a younger ice cover [Maslanik et al., 2011]. Specific factors that determine the temporal distribution of sea ice are poorly understood because few observations of key variables have been made in the central Arctic. For example, the planetary boundary layer (PBL), the lowest part of the atmosphere governed by interaction with Earth's surface, plays a critical role involving the exchange of momentum, heat, water vapor, trace gases, and aerosol particles. Satellites can provide limited observations of sea ice properties, but so far, accurate measurements of ice thickness or boundary layer properties have not been easily obtained. Although satellite retrievals of geophysical variables might be an essential source of information, their reliability remains questionable owing to inadequate spatial and/or temporal resolution and to a need for further validation.

The Whistler Aerosol and Cloud Study (WACS 2010), included intensive measurements of trace gases and particles at two sites on Whistler Mountain. Between 6-11 July 2010 there was a sustained high-pressure system over the region with cloud-free conditions and the highest temperatures of the study. During this period, the organic aerosol concentrations rose from < 1 mu g m(-3) to similar to 6 mu g m(-3). Precursor gas and aerosol composition measurements show that these organics were almost entirely of secondary biogenic nature. Throughout 6-11 July, the anthropogenic influence was minimal with sulfate concentrations < 0.2 mu g m(-3) and SO2 mixing ratios approximate to 0.05-0.1 ppbv. Thus, this case provides excellent conditions to probe the role of biogenic secondary organic aerosol in aerosol microphysics. Although SO2 mixing ratios were relatively low, box-model simulations show that nucleation and growth may be modeled accurately if J(nuc) = 3 x 10(-7)[H2SO4] and the organics are treated as effectively non-volatile. Due to the low condensation sink and the fast condensation rate of organics, the nucleated particles grew rapidly (2-5 nm h(-1)) with a 10-25% probability of growing to CCN sizes (100 nm) in the first two days as opposed to being scavenged by coagulation with larger particles. The nucleated particles were observed to grow to similar to 200 nm after three days. Comparisons of size-distribution with CCN data show that particle hygroscopicity (kappa) was similar to 0.1 for particles larger 150 nm, but for smaller particles near 100 nm the kappa value decreased near midway through the period from 0.17 to less than 0.06. In this environment of little anthropogenic influence and low SO2, the rapid growth rates of the regionally nucleated particles - due to condensation of biogenic SOA - results in an unusually high efficiency of conversion of the nucleated particles to CCN. Consequently, despite the low SO2, nucleation/growth appear to be the dominant source of particle number.

Atmospheric emissions of gas and particulate matter from a large ocean-going container vessel were sampled as it slowed and switched from high-sulfur to low-sulfur fuel as it transited into regulated coastal waters of California. Reduction in emission factors (EFs) of sulfur dioxide (SO2), particulate matter, particulate sulfate and cloud condensation nuclei were substantial (>= 90%). EFs for particulate organic matter decreased by 70%. Black carbon (BC) EFs were reduced by 41%. When the measured emission reductions, brought about by compliance with the California fuel quality regulation and participation in the vessel speed reduction (VSR) program, are placed in a broader context, warming from reductions in the indirect effect of SO4 would dominate any radiative changes due to the emissions changes. Within regulated waters absolute emission reductions exceed 88% for almost all measured gas and particle phase species. The analysis presented provides direct estimations of the emissions reductions that can be realized by California fuel quality regulation and VSR program, in addition to providing new information relevant to potential health and climate impact of reduced fuel sulfur content, fuel quality and vessel speed reductions.

The mass transport budgets of 1,1,1-trichloro-2,2-bis(chlorophenyl)ethane (p,p'-DDT) and decabromodiphenyl ether (BDE-209) in the Pearl River Delta, South China were calculated based on previously collected data. Residual p,p'-DDT, mostly related to historical use, has largely settled into soil (780,000 kg), while the soil BDE-209 inventory (44,000 kg) is considerably smaller. Conversely, large amounts of BDE-209 currently used in numerous commercial products have resulted in a much higher atmospheric depositional flux of BDE-209 (28,100 kg/yr) relative to p,p'-DDT (310 kg/yr). The soil inventory of p,p'-DDT is predicted to decrease to half of its current value after 22 years, and the percent area containing soil p,p'-DDT at levels exceeding the effects range medium (27 ng/g) will decrease from 40% to 20%. Finally, soil BDE-209 inventory will reach an equilibrium value of 940 tons in 60 years, when BDE-209 levels in 50% of soil will be above an equivalent risk guideline value (125 ng/g). (C) 2011 Elsevier Ltd. All rights reserved.

Daily to weekly integrated PM2.5 samples were collected consecutively from August 2005 through November 2007 at Egbert, a rural site in southern Ontario with two collocated samplers to characterize temporal variations of organic and elemental carbon (OC and EC) concentrations and to review the effects of different sampling intervals on their respective concentrations. OC and EC concentrations from both samplers had reasonable agreements for the samples with identical sampling intervals, whereas for the samples with different sampling intervals, they did not coincide. Considering sampling artifacts, analytical challenges and highly varied daily concentrations, it is suggested and would be advantageous to adopt the weekly integrated sampling strategy other than 29-h sampling on selected days for long-term trend studies on ambient carbonaceous PM. Both OC and EC concentrations varied seasonally by factors of 2.4 and their concentrations in warm seasons (May-October) were higher than those in cold seasons (November-April). Greater fluctuations were also found in warm seasons during the study period. Weekly concentrations of carbonaceous species at Egbert and urban Toronto show similar temporal variations and small urban excess during the one-year parallel sampling period, indicating a relatively large regional contribution from transport instead of local emissions to the paired urban-rural sites. The continental background level of total carbon mass (TCM) in PM2,5 in southern Ontario, constrained by surface air mass directions and back trajectories, was estimated to be 0.5 mu g m(-3). It is likely that the elevated OC level during the warm season in 2007 compared with those in 2006 was due to more smog days in 2007. (C) 2011 Elsevier Ltd. All rights reserved.

Concentrations of dichlorodiphenyltrichloroethane (DDT) and its metabolites (designated as DDTs, the sum of o,p'- and p,p'-DDT, o,p'- and p,p'-DDE, and o,p'- and p,p'-DDD) in air and precipitation from the Pearl River Delta (PRD) of China were determined. Total concentrations of DDTs in air (gas + particle) and precipitation (dissolved + particle) were 170 +/- 120 pg m(-3) and 940 +/- 180 pg L(-1) for Dongguan (rural) and 240 +/- 120 pg m(-3) and 790 +/- 140 pg L(-1) for Shunde (rural), respectively, while they were 1550 +/- 640 pg L(-1) in precipitation from Guangzhou (urban). Log-transformed partition coefficients between air and particulate organic matter (log K'(oa)) of p,p'-DDT, p,p'-DDE, p,p'-DDD, o,p'-DDT, o,p'-DDE, and o,p'-DDD were 9.64 +/- 0.58, 10.07 +/- 0.56, 9.90 +/- 0.76, 10.06 +/- 0.66, 10.02 +/- 0.72, and 10.13 +/- 0.57, respectively: while those between water and particulate organic matter (log K'(om)) were 6.58 +/- 0.66, 6.36 +/- 0.53, 6.01 +/- 0.62, 6.41 +/- 0.42, 5.98 +/- 0.76, and 5.95 +/- 0.66, respectively. Total washout ratios by bulk rainfalls ranged from 4600 for o,p'-DDT to 54,000 for p,p'-DDT. Estimated average dry particle and wet depositional intensities in the PRD were 2.1 x 10(-6) and 1.6 x 10(-6) g m(-2) y(-1). (C) 2011 Elsevier Ltd. All rights reserved.

Xylenes are important constituents of many liquid fuels, as well as precursors of secondary organic aerosols (SOAs). To examine the mechanisms for formation of SOAs in the atmosphere, the abstraction reaction of p-xylene with OH and the secondary degradation channels of its intermediates were first and extensively investigated with density functional theory at the B3LYP/6-31+G (d, p) level. The result indicates that H-abstraction from methyl groups is a barrier-less path while that from phenyl groups require a free energy barrier of approximately 2.8 kcal mol(-1). Upon formation of p-xylyl, further addition by O-2 readily occurs to form peroxy radical. Subsequently, possible degradation channels for the formation of main products (p-tolualdehyde and p-quinone methide) have been determined in presence of NO. The free energy profile constructed shows that the entire reaction process is exothermic. In addition, the dipole moment of p-tolualdehyde is higher than that of p-xylene, consistent with their relative hygroscopic values. This indicates that the degradation products of p-xylene can readily immerse into the SOA phase, while p-xylene may be subject to further atmospheric degradation to form non-volatile compounds. (C) 2011 Elsevier B.V. All rights reserved.

Studies have demonstrated that cis-pinonic acid (CPA) is an important product from the oxidation of pinenes with ozone. CPA has been measured on aerosols and is used as an aging indicator for secondary organic aerosols (SOA). CPA levels and formation in urban aerosols and its annual variability, however, are still poorly understood. Here, we present monthly CPA average concentrations on aerosols in Toronto, Ontario, Canada based on a two-year-period: 2000-2001. They displayed a seasonal pattern associated with temperature and ozone (O(3)) plus nitrogen dioxide (NO(2)) reflecting the influence these have on emissions of pinenes from forests and their atmospheric oxidation, respectively. However, in Toronto some months with higher CPA concentrations, especially in the winter, were inconsistent with the seasonality of temperature or/and O(3) + NO(2) levels. Instead these deviations were associated with increases in wood burning tracers such as dehydroabietic acid (DHAA) and sugars. Similar features were observed during a two-week-period comparing day and nighttime CPA concentrations in the Lower Fraser Valley (LFV) of British Columbia, Canada, in that the CPA concentrations clearly varied diurnally with temperature and O(3) + NO(2) on some days, but also showed a significant correspondence with variations in the wood burning tracer concentrations, such as levoglucosan. These findings demonstrate that CPA formation is strongly impacted by wood burning activity. Crown Copyright (C) 2011 Published by Elsevier Ltd. All rights reserved.

Observations from four periods (three late springs and one early summer) at temperate forest sites in western and eastern Canada offer the first estimation of how the concentrations of submicron forest organic aerosol mass (SFOM) from the oxidation of biogenic volatile organic compounds (BVOC) vary over the ambient temperature range of 7 degrees C to 34 degrees C. For the measurement conditions of clear skies, low oxides of nitrogen and within approximately one day of emissions, 50 estimates of SFOM concentrations show the concentrations increase exponentially with temperature. The model that is commonly used to define terpene emissions as a function of temperature is able to constrain the range of the SFOM values across the temperature range. The agreement of the observations and model is improved through the application of an increased yield of SFOM as the organic mass concentration increases with temperature that is based on results from chamber studies. The large range of SFOM concentrations at higher temperatures leaves open a number of questions, including the relative contributions of changing yield and of isoprene, that may be addressed by more ambient observations at higher temperatures. Crown Copyright (C) 2011 Published by Elsevier Ltd. All rights reserved.

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+/SO42- 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 x 10(-3)-2 x 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.

As part of the BAQS-Met 2007 field campaign, Aerodyne time-of-flight aerosol mass spectrometers (ToF-AMS) were deployed at two sites in southwestern Ontario from 17 June to 11 July 2007. One instrument was located at Harrow, ON, a rural, agriculture-dominated area approximately 40 km southeast of the Detroit/Windsor/Windsor urban area and 5 km north of Lake Erie. The second instrument was located at Bear Creek, ON, a rural site approximately 70 km northeast of the Harrow site and 50 km east of Detroit/Windsor. Positive matrix factorization analysis of the combined organic mass spectral dataset yields factors related to secondary organic aerosol (SOA), direct emissions, and a factor tentatively attributed to the reactive uptake of isoprene and/or condensation of its early generation reaction products. This is the first application of PMF to simultaneous AMS measurements at different sites, an approach which allows for self-consistent, direct comparison of the datasets. Case studies are utilized to investigate processing of SOA from (1) fresh emissions from Detroit/Windsor and (2) regional aerosol during periods of inter-site flow. A strong correlation is observed between SOA/excess CO and photochemical age as represented by the NOx/NOy ratio for Detroit/Windsor outflow. Although this correlation is not evident for more aged air, measurements at the two sites during inter-site transport nevertheless show evidence of continued atmospheric processing by SOA production. However, the rate of SOA production decreases with airmass age from an initial value of similar to 10.1 mu g m(-3) ppmv(CO)(-1) h(-1) for the first similar to 10 h of plume processing to near-zero in an aged airmass (i.e. after several days). The initial SOA production rate is comparable to the observed rate in Mexico City over similar timescales.

Measurements of submicron aerosol chemical composition were made over the central Arctic Ocean from 5 August to 8 September 2008 as a part of the Arctic Summer Cloud Ocean Study (ASCOS) using an aerosol mass spectrometer (AMS). The median levels of sulphate and organics for the entire study were 0.051 and 0.055 mu gm(-3), respectively. Positive matrix factorisation was performed on the entire mass spectral time series and this enabled marine biogenic and continental sources of particles to be separated. These factors accounted for 33% and 36% of the sampled ambient aerosol mass, respectively, and they were both predominantly composed of sulphate, with 47% of the sulphate apportioned to marine biogenic sources and 48% to continental sources, by mass. Within the marine biogenic factor, the ratio of methane sulphonate to sulphate was 0.25+/-0.02, consistent with values reported in the literature. The organic component of the continental factor was more oxidised than that of the marine biogenic factor, suggesting that it had a longer photochemical lifetime than the organics in the marine biogenic factor. The remaining ambient aerosol mass was apportioned to an organic-rich factor that could have arisen from a combination of marine and continental sources. In particular, given that the factor does not correlate with common tracers of continental influence, we cannot rule out that the organic factor arises from a primary marine source.

Aerosol fluxes were measured above a mixed forest by Eddy Covariance (EC) with a Fast Mobility Particle Sizer (FMPS) at the Borden Forest Research Station in Ontario, Canada between 13 July and 12 August 2009. Chemically speciated flux measurements were made at a height of 29m at the same location between 19 July and 2 August, 2006 using a Quadrupole Aerosol Mass Spectrometer (Q-AMS). The Q-AMS measured an average sulphate deposition velocity of 0.3mms(-1) and an average nitrate deposition velocity of 4.8mms(-1). The FMPS, mounted at a height of 33m (approximately 10m above the canopy top) and housed in a temperature controlled enclosure, measured size-resolved particle concentrations from 3 to 410 nm diameter at a rate of 1 Hz. For the size range 18 < D < 452 nm, 60% of fluxes were upward. The exchange velocity was between -0.5 and 2.0 mms(-1), with median values near 0.5 mms(-1) for all sizes between 22 and 310 nm. The size distribution of the apparent production rate of particles at 33m peaked at a diameter of 75 nm. Results indicate a decoupling of the above and below canopy spaces, whereby particles are stored in the canopy space at night, and are then diluted with cleaner air above during the day.