Dust and Black Carbon in Seasonal Snow Across Northern China

DUST AND BLACK CARBON IN SEASONAL SNOW ACROSS NORTHERN CHINA Snow is the most reflective natural surface on Earth. Its albedo (the fraction of sunlight reflected) can be reduced by small amounts of dark impurities such as dust and black carbon (BC) particles. This effect is significant for climate and the hydrological cycle. BC has previously been measured in Arctic snow, but it now appears that the larger effect may be in the midlatitudes because snow at lower latitudes is exposed to more sunlight and is closer to the sources of BC. A field campaign was conducted across northern China in January and February 2010. Snow samples were collected at 46 sites in six provinces. The absorbing impurities are principally dust and BC particles in northwestern and northeastern China, respectively. The estimated concentration of BC is only 30-50 ppb in the far north of Heilongjiang Province (51 degrees N), which is not much more than that found along the coast of the Arctic Ocean, 2,000 km farther north, but it increases to several hundred parts per billion in heavily industrialized Liaoning Province, Jilin Province, and the southern part of Heilongjiang. The BC content of snow in northeast China is comparable to values found in Europe (20-800 ppb). The steep drop-off in BC content of snow with latitude may indicate that little BC emitted in China in the winter is exported northward to the Arctic.