[Influence of season change on the level of heavy metals in outdoor settled dusts in different functional areas of Guiyang City].

To study the influence of season change on the level of heavy metal in outdoor settled dusts at both city and functional area scale, dust samples were collected in July 2010 and February 2011 from different functional areas in the Guiyang City. The results showed that among all heavy metal elements involved, Pb and As were most significantly affected by season change, with a significantly higher amount in winter than in summer, mostly accumulated in smaller particles of dust. Functional areas where heavy metal concentrations were most significantly affected by seasons were city square and school area, and followed by residential area. Elements that showed the greatest difference in distribution pattern in different fractions between summer and winter were As and Pb, while the functional areas that were most severely influenced were city square and school area, followed by residential area. The isotopic ratio analysis showed that the Pb in the outdoor settled dust in Guiyang was partly contributed by Diesel exhaust dust, paint chip and soil. Summer precipitation, coal-burning in winter and temperature difference between summer and winter may contribute to the seasonal change of the level of Pb and As in the dusts.