Arctic haze: current trends and knowledge gaps

Abstract

Trend analyses were performed on several indicators of Arctic haze using data from sites located in the North American, Norwegian, Finnish and Russian Arctic for the spring months of March and April. Concentrations of nonseasalt (nss) SO 4 = in the Canadian, Norwegian and Finnish Arctic were found to have decreased by 30-70% from the early 1990s to present. The magnitude of the decrease depended on location. The trend in nss SO 4 = at Barrow, Alaska from 1997 to present, is unclear. Measurements at Barrow of light scattering by aerosols show a decrease of about 50% between the early 1980s and the mid-1990s for both March and April. Restricting the analysis to the more recent period of 1997 to present indicates an increase in scattering of about 50% during March. Aerosol NO 3 − measured at Alert, Canada has increased by about 50% between the early 1990s and 2003. Nss K + and light absorption, indicators of forest fires, have a seasonal maximum during the winter and spring and minimum during the summer and fall at both Alert and Barrow. Based on these data, the impact of summertime forest fire emissions on low-altitude surface sites within the Arctic is relatively small compared to winter/spring emissions. Key uncertainties about the impact of long range transport of pollution to the Arctic remain including the certainty of the recent detected trends; sources, transport and trends of soot; and radiative effects due to complex interactions between aerosols, clouds and radiation in the Arctic.

Ice sheets and nitrogen

“…Finally, a record from Severnaya Zemlya, north of Russia at 958 E [25], shows a rapid increase in nitrate concentration in the 1960s, followed by a slower decline, and appears to be more closely related to regional emissions of NO x from the Siberian Arctic. Taken together all these records indicate that the Arctic atmosphere is strongly affected by anthropogenic NO x emissions originating further south, in line with understanding gained from studies of Arctic Haze [26]. In contrast to Greenland, data from Antarctica, although showing considerable year-to-year noise, show no significant trend over the twentieth century ( [20,21]; figure 2).…”

An update on polar aerosol optical properties using POLAR-AOD and other measurements performed during the International Polar Year

“…Only more recently, they have been predominantly ascribed to the transport of polluted-air masses of industrial origin from North America, Europe and Asia, and biomass burning particles generated by agricultural activities and/or boreal forest fires. In view of increasing aerosol emissions in the Asian area, Quinn et al (2007) pointed out that it is reasonable to expect a corresponding increase in the frequency and intensity of AH episodes within a few years. However, while emission rates certainly exert an influence on the distribution of haze, changes in atmospheric transport were also a relevant factor, because atmospheric circulation has undergone significant changes in the Arctic region over the last decades, leading to variations in atmospheric circulation patterns affecting cloudiness features, temperature conditions and snowfall frequency (Stone, 1997;Stone et al, 2002).…”

“…Subsequently, only the data relative to the four summer months from June to September were considered when calculating the long-term variations of AOD, with the background contribution hereafter referred to as BG, and enhancements attributed to extinction mainly by smoke particles from boreal forest fires (hereafter referred to as FFS) in North America and Siberia (Forster et al, 2001;Damoah et al, 2004;Stohl et al, 2006;Tunved et al, 2006). Following the same approach used by Tomasi et al (2007), this summer-time analysis ignores influences of AH and/or Asian dust (AD) that occur mainly during late winter and spring (Rahn et al, 1977;Shaw, 1982Shaw, , 1983VanCuren and Cahill, 2002;Stone et al, 2007;Quinn et al, 2007). Tomasi et al (2007) showed that the summer BG aerosol cases are distinguishable in terms of AOD from signatures of AH, AD and FFS events: the values of AOD(500 nm) measured for AH, AD and FFS cases in general exceed 0.10 and are appreciably lower under typical background conditions, while exponent a can assume values varying over the range between about 0.5 and 2.0 and are sometimes difficult to use to distinguish aerosol types, although Stone (2002) and Treffeisen et al (2007) suggested spectral signatures of AOD useful for identifying different types of Arctic aerosol.…”

“…For this purpose, an evaluation of the mass fractions of the main particulate chemical components was performed, by taking into account the results found by Quinn et al (2002), who examined a 3-year set of simultaneous measurements of aerosol chemical composition and light scattering and absorption measurements performed at Barrow from October 1997 to December 2000, for rather low relative humidity conditions. These estimates were given by Quinn et al (2007) in terms of monthly mean concentrations of aerosol mass constituents, such as sea salt, non-sea salt (nss) sulphate, methane sulphonic acid (MSA), ammonium ions, and nss K, Mg and Ca ions, for both the submicron and supermicron size ranges. In the present study, the above data were integrated by (i) the estimates of total carbon (black carbon (BC) þ organic carbon (OC)) concentration measured by Sharma et al (2002Sharma et al ( , 2006 at Barrow, and (ii) the conversion from the above nss Mg and Ca ionic concentrations to the AleSi components, using the soil factors proposed by Polissar et al (1998) for the Northwest Alaska areas.…”

Springtime Arctic aerosol: Smoke versus haze, a case study for March 2008

“…In the Arctic troposphere increased aerosol loads can occur during spring, a phenomenon which is called Arctic Haze (Quinn et al, 2007). The radiation impact of this aerosol is still poorly understood.…”