Seasonal variation of aerosol water uptake and its impact on the direct radiative effect at Ny-Ålesund, Svalbard

© Author(s) 2014. This work is distributed under the Creative Commons Attribution 3.0 LicenseIn this study we investigated the impact of water uptake by aerosol particles in ambient atmosphere on their optical properties and their direct radiative effect (ADRE, W m-2) in the Arctic at Ny-Ålesund, Svalbard, during 2008. To achieve this, we combined three models, a hygroscopic growth model, a Mie model and a radiative transfer model, with an extensive set of observational data. We found that the seasonal variation of dry aerosol scattering coefficients showed minimum values during the summer season and the beginning of fall (July-August-September), when small particles (< 100 nm in diameter) dominate the aerosol number size distribution. The maximum scattering by dry particles was observed during the Arctic haze period (March-April-May) when the average size of the particles was larger. Considering the hygroscopic growth of aerosol particles in the ambient atmosphere had a significant impact on the aerosol scattering coefficients: the aerosol scattering coefficients were enhanced by on average a factor of 4.30 ± 2.26 (mean ± standard deviation), with lower values during the haze period (March-April-May) as compared to summer and fall. Hygroscopic growth of aerosol particles was found to cause 1.6 to 3.7 times more negative ADRE at the surface, with the smallest effect during the haze period (March-April-May) and the highest during late summer and beginning of fall (July-August-September).Peer reviewe

Hygroscopic growth and cloud forming potential of Arctic aerosol based on observed chemical and physical characteristics (a 1 year study 2007-2008)

Aerosol particle samples were collected, and the particle size distribution was measured during 1 year at the Zeppelin station (474 m asl) on Svalbard. The chemical constituents, hygroscopicity, and cloud forming properties of the aerosol were analyzed. The aerosol contained mostly sulfate and nitrate during the summer, whereas from September to February the main components were sodium and chloride. The highest concentration (20%) of water-soluble organic matter was sampled in December. The hygroscopic growth factors for the water-soluble fraction were 1.56-2.01 at 90% relative humidity, peaking in October, when the measured supersaturations needed for cloud drop formation were also the lowest. Sea-salt components showed a positive correlation with the cloud forming capability, whereas the organic content had no correlation. The hygroscopicity factors, or kappa values, were determined in three ways for each month: (1)kappa(H-TDMA) from measurements of the hygroscopic growth of particles produced from atomization of the filter extracts, (2)kappa(CCNC) from measurements of the critical supersaturation as a function of size for these particles, and (3)kappa(chem) was modeled based on the organic and inorganic composition of the filter samples. Using the measured particle size distributions and the critical activation diameters from the Cloud Condensation Nuclei Counter (CCNC) measurements, it was found that the number of CCN varied more with supersaturation during the summer months. The best agreement between all three kappa values was in December and January. Comparisons with earlier studies do not suggest any trend in the Arctic aerosol seasonal variability over the last decade

Real-world traffic emission factors of gases and particles measured in a road tunnel in Stockholm, Sweden

Measurements in a road tunnel in Stockholm, Sweden give the real-world traffic emission factors for a number of gaseous and particle pollutants. These include 49 different polycyclic aromatic hydrocarbons (PAH), CO, NOX, benzene, toluene, xylenes, aldehydes, elements and inorganic/organic carbon contained in particles, the sub-micrometer aerosol number size distribution, PM2.5 and PM10. The exhaust pipe emission factors are divided with the help of automated traffic counts into the two pollutant sources, the heavy-duty vehicles (HDV) and light-duty vehicles (LDV). The LDV fleet contains 95% petrol cars and the total fleet contains about 5% HDV. When data permitted, the emission factors were further calculated at different vehicle speeds. The current work shows that average CO, NOX and benzene emission factors amounted to 5.3, 1.4 and 0.017 g veh(-1) km(-1), respectively. Since the mid-90s CO and benzene decreased by about 15%, carbonyls by about a factor 2, whereas NOX did not change much. PAR emission factors were 2-15 times higher than found during dynamometer tests. Most particles are distributed around 20 nm diameter and the LDV fleet contributes to about 65% of both PM and particle number. In general, the gaseous emissions are higher in Sweden than in USA and Switzerland, foremost due to the lower fraction catalytic converters in Sweden. The PM and number emissions of particles are also slightly higher in the Swedish tunnel. (C) 2003 Elsevier Ltd. All rights reserved

Chemical and physical characterization of emissions from birch wood combustion in a wood stove

The purpose of this study was to characterize the emissions of a large number of chemical compounds emitted from birch wood combustion in a wood stove. Birch wood is widely used as fuel in Swedish household appliances. The fuel load was held constant during six experiments. Particles < 2.5 mum diameter were collected and the size distribution of the particles was measured. The results were compared to the size distribution in road traffic emissions. It could be seen that the number distribution differed between the sources. In traffic exhaust, the number of particles maximized at 20 nm, while the number distribution from wood burning ranged from 20 to 300 nm. The ratio K/Ca on particles was found. to be significantly different in wood burning compared to road dust, range 30-330 for the former and 0.8+/-0.15 for the latter. The source profile of common elements emitted from wood-burning differed from that found on particles at a street-level site or in long-distance transported particles. The ratio toluene/benzene in this study was found to be in the range 0.2-0.7, which is much lower than the ratio 3.6+/-0.5 in traffic exhaust emissions. Formaldehyde and acetone were the most abundant compounds among the volatile ketones and aldehydes. The emission factor varied between 180-710mg/kg wood for formaldehyde and 5-1300mg/kg wood for acetone. Of the organic acids analyzed (3,4,5)-trimethoxy benzoic acid was the most abundant compound. Of the PAHs reported, fluorene, phenanthrene, anthracene, fluoranthene and pyrene contribute to more than 70% of the mass of PAH. Of the elements analyzed, K and Si were the most abundant elements, having emission factors of 27 and 9mg/kg wood, respectively. Although fluoranthene has a toxic equivalence factor of 5% of benzo(a)pyrene (B(a)P), it can be seen that the toxic potency of fluoranthene in wood burning emissions is of the same size as B(a)P. This indicates that the relative carcinogenic potency contribution of fluoranthene in wood smoke would be about 40% of B(a)P. (C) 2002 Elsevier Science Ltd. All rights reserved