Measurements of optical properties of atmospheric aerosols in Northern Finland

Abstract

Abstract. Three years of continuous measurements of aerosol optical properties and simultaneous aerosol number size distribution measurements at Pallas GAW station, a remote subarctic site in the northern border of the boreal forest zone, have been analysed. The scattering coefficient at 550 nm varied from 0.2 to 94.4 Mm −1 with an average of 7.1±8.6 Mm −1 . Both the scattering and backscattering coefficients had a clear seasonal cycle with an autumn minimum and a 4-5 times higher summer maximum. The scattering was dominated by submicron aerosols and especially so during late summer and autumn. TheÅngström exponent had a clear seasonal pattern with maximum values in late summer and minimum values during wintertime. The highest hemispheric backscattering fraction values were observed in autumn. To analyse the influence of air mass origin on the aerosol optical properties a trajectory climatology was applied to the Pallas aerosol data. The most polluted trajectory patterns represented air masses from the Kola Peninsula, Scandinavia and Russia as well as long-range transport from Britain and Eastern Europe. These air masses had the largest average scattering and backscattering coefficients for all seasons. Higher than average values of theÅngström exponent were also observed in connection with transport from these areas.

Seasonality of aerosol optical properties in the Arctic

“…This same SAE seasonality at BRW was also observed in previous studies (Bodhaine, 1983;Delene and Ogren, 2002), and one study offers an explanation as to this seasonality with observations of an increase in sea salt when the sea ice melts in summer months (Quinn et al, 2002). PAL has a different seasonality, with highest SAE values in the summer and lowest SAE values in the winter and early spring, which agrees with findings from Aaltonen et al (2006) and Lihavainen et al (2015). The statistics of SAE in Table 2 show an average SAE of 1.66 at PAL, which is close to the average of 1.7±0.7 that is reported in Lihavainen et al (2015) and the median of 1.8 reported by Pandolfi et al (2018).…”

“…A more detailed description of aerosol optical measurements and sampling can be found in Lihavainen et al (2015) and in Backman et al (2017). A climatology of aerosol optical properties at PAL is presented by Aaltonen et al (2006) and Lohila et al (2015).…”

“…The low summertime values of absorption and scattering currently observed in the Arctic are likely to be particularly vulnerable to warmer, drier climatic conditions (e.g., due to increases in summertime forest fires and decreases in sea ice leading to enhanced marine emissions and human activities in the region during the summer). Published climatologies and seasonal cycles of in situ Arctic intensive aerosol prop-erties (i.e., properties that are ratios of extensive properties and not directly dependent on aerosol amount) are sparse and suggest that, unlike the relatively consistent seasonal pattern for extensive properties, the seasonal cycles of intensive optical properties (e.g., Ångström exponent) may differ from site to site (Delene and Ogren, 2002;Aaltonen et al, 2006;Lihavainen et al, 2015). This work seeks to expand on previous aerosol optical analyses in the Arctic by synthesizing aerosol seasonality at multiple Arctic stations and adding new knowledge on the seasonality of intensive aerosol characteristics in the region.…”

Long-term measurements of aerosol and carbon monoxide at the ZOTTO tall tower to characterize polluted and pristine air in the Siberian taiga

“…The medians and averages suggest, however, that the aerosol sampled at ZOTTO during our study period were generally representative of a fairly clean region. Our average values for the total scattering coefficient (σ sp ) and the back scattering coefficient (σ bsp ) at the ZOTTO site are comparable to those measured at other high latitude Northern Hemisphere remote sites using the same type of instrument (TSI 3563), including three years of measurements at Barrow, Alaska (Delene and Ogren, 2002), and three years of measurements made at Pallas, in northern Finland (Aaltonen et al, 2006). Much larger scattering coefficients (typically by 1-2 orders of magnitude) have been measured at sites affected by urban or continental pollution (Cabada et al, 2004;Vrekoussis et al, 2005;Garland et al, 2009).…”

Variability of aerosol optical properties in the Western Mediterranean Basin

“…Scattering and absorption coefficients with mean values higher than 700 Mm −1 and 80 Mm −1 respectively were measured in a highly polluted site close to New Delhi (Hyvärinen et al, 2010). In Artic remote sites mean scattering and absorption coefficients lower than 10 Mm −1 and 1 Mm −1 , respectively were measured (Aaltonen et al, 2006;Delene and Ogren, 2002 (Lyamani et al, 2006). Recently, mean scattering and backscattering coefficients of 42.5 Mm −1 and 5.9 Mm −1 respectively were measured in a small city quite far from pollution sources in the southwestern Portugal (Pereira et al, 2011).…”