In the early 1970’s, I noticed the optical depth of the atmosphere at Barrow, Alaska was quite high. Given the isolated location of this station on Alaska’s northern tip (72 degrees N) I had expected that the turbidity would be low, around 0.05. Instead found values twice or three times that magnitude. Moreover the optical depth varied strongly with wavelength, being larger at shorter wavelengths, which suggested that the particles causing the atmospheric contamination were small, probably sub micron in diameter.  From this it could be deduced that the particles were not blown dust from river cuts or suspended ice crystals.  It seemed likely they were related to industrial air pollution, but no sources except a very minor one is within hundreds of miles.  Furthermore, the strange and unknown haze seemed to grow stronger in northerly winds. This was most peculiar indeed because only the Arctic Ocean, with its cover of pack ice, is north of Barrow.

Further investigation, made with a sun photometer carried aloft in a Bush aircraft showed the layers sometimes had complicated vertical structure, sometimes showing distinct bands and were most frequently in the altitude zone from 500m to about 3 km. In addition, the layers were horizontally homogeneous over distances of hundreds of km and showed no signs of being affiliated with leads or cracks in the pack ice. Back trajectory analysis carried out at the 850 mb level suggested that this air had passed over eastern Europe/Western Soviet Union about ten days earlier. At that time, transport of anthropogenic material over such vast distances (3,000 km) was thought to be impossible, except possibly for volcanic plume emissions injected into the upper troposphere/lower stratosphere.

I met Kenneth Rahn of the University of Rhode Island at a meeting in Reno in 1975 and told him the story about the strange layers in the Arctic.  Ken at the time was investigating heavy metal signatures in polluted layers with the neutron activation method at the URI reactor.  He was intrigued and so we wrote a small proposal and submitted it to Office of Naval Research, which had an interest in Arctic matters around the Barrow area.  Under ONR sponsorship we collected more than a year of weekly high volume filters at Barrow and found to our great surprise that indeed the air did seem to be polluted, most especially during the spring months.  In summer the atmospheric aerosol concentrations dropped to very low values.  About this time I also discovered that my colleague Gerd Wendler had made regular semi broad band turbidity measurements with a Linke Feussner Actinometer at or near McCall Glacier in the Brooks Range in northern Alaska. Indeed, these also showed turbidity maxima during the late winter/early spring months. 

In the spring months of 1977 we carried out specific investigations of the haze chemistry using a Cessna 180 aircraft equipped with a high volume sampling system.  We learned from this investigation that the layers were crustal material, resembling desert dust microscopically and minerologically. We speculated, correctly that the layers had formed from dust storms in the Gobi and Takla Makan deserts in Asia. Indeed back trajectory analysis supported this conclusion.  And though this conclusion was published in Nature in what we now call our “Red Herring Paper,” it turned out the sampling had occurred during a rather unusually strong and somewhat rare synoptic system favoring the transport of desert dust to Alaska.  Both the wavelength dependence of the optical depth and the trace elemental signature differed from samples taken during more usual springtime meteorological conditions.

Further investigation of the chemical and physical properties of the aerosols, along with back trajectory analyses, convinced us that the more usual springtime Arctic Haze is primarily emanating from anthropogenic sources, especially from smelting activities in eastern Europe and western and northern USSR.  Of great interest in helping us to firm up this conclusion was the usage of the V/NC Mn ratio, where NC Mn is the estimated non-crustal component of manganese. We had found that this ratio is considerably higher for aerosol sources in North America, which is primarily an oil-based economy, than it is in Eurasia, based more on coal burning technology that time.  

Expansion of the research by investigators in the Canadian Arctic, especially by Len Barrie’s group, and by investigators in Scandinavia, especially by B. Ottar at the Norwegian Institute for Atmospheric Research (NILU) and others eventually showed quite clearly that Arctic Haze is most common and strongest within the Arctic Airmass, roughly bounded by a weak meteorological feature known as the Arctic Front. The Arctic Airmass is quite small in extent and sometimes even disappears in summer, but grows larger and larger throughout winter, reaching a two lobe structure dipping down over Eurasia and North America in late winter/early spring. It is this air mass that becomes rather homogeneously polluted, due to its aerial over-cover of strong pollution sources, such as metal smelters, and to the rather low rate of aerosol removal in this dry, stable air mass system.

Several international conferences were held on Arctic Haze and it continues to be investigated and classified by surface based stations, airborne studies, such as the ARCTAS experiment in 2009, and by satellite borne sensors.  

It is believed that generally Arctic Haze has a small positive climate forcing impact (warming), of approximately one watt/ square meter for the earth-atmosphere system. This is mainly due to a combination of slight aerosol absorption from soot aerosol, and multi reflections of the radiation streams between the haze and underlying bright surface.  The climatic effect on the surface itself is one of slight cooling. There has been speculation that Arctic Haze impacts formation and dissipation of thin Arctic stratus cloud systems, due to alterations in the cloud condensation nuclei activation.  This remains to be studied more intensely.  It appears that Arctic Haze has generally decreased in intensity since the breakup of the Soviet Union in 1989, but that there may be increasing quantities of Gobi dust and anthropogenic pollution from the China mainland, no doubt associated with the industrial growth currently taking place in China. 

Further information on Arctic Haze can be found at the wikipedia page on Arctic Haze

References: 

P. K. Quinn, G. Shaw, E. Andrews, E, Dutton, T. Ruoho-Airola and S. Gong., Arctic Haze:  current trends and knowledge gaps, Tellus 59B ,99-114, 2007.

Shaw, G., The Arctic haze phenomenon, Bull. Am Met. Soc, 76, 2403-2413, 1987

Shaw, G., Evidence for a central Eurasian source area of Arctic haze in Alaska, Nature, 299, 815-818, 1983.

Shaw, G., The vertical distribution of atmospheric aerosols at Barrow, Alaaska, Tellus 27, 39-50, 1975.

Shaw, G., Aerosol chemical components in Alaska air masses 1. Aged pollution and 2. sea salt and marine products, J. Geophy Res., 96, 22,357-22,372, 1981

Rahn, K, R. Borys and G. Shaw, The Asian source of Arctic haze bands. Nature 268, 713-715, 1977