Characteristics of ambient 1-min PM 2.5 variation in Beijing.

One-minute PM(2.5) concentration was obtained with LD-5C pocket microcomputer laser dust instrument from Dec. 15th, 2005 to Jan. 16th, 2006 and Mar. 17th to Apr. 28th, 2006 in Beijing. The concentration of SO(2), NO(2), O(3), CO, and PM(10) from Jan. 1st, 2001 to Dec. 31st, 2004 were obtained from the conversion of air pollution index. Results showed that all the pollutants showed cyclic characteristics. The longer yearly cycles was shown from SO(2), NO(2), O(3), CO, and PM(10), as the sampling time was 4-year long and daily collected. The shorter hourly and daily cycle was shown from 1-min PM(2.5), as the sampling time was about 1-month long and one collected at 1 min. The spectral density analysis confirmed this from the periodogram graphs. The longer yearly cycle (365, 180 days), the seasonal cycle (120, 60-90 days), and monthly cycle (21, 23, 27 days) of SO(2), NO(2), CO, O(3), and PM(10) were obviously shown. In addition, the shorter weekly cycle of 5-7 days is obviously shown, too. The shorter hourly cycle (8-12, 4-6, 3, 1-2 h, 20 min) of 1-min PM(2.5) was also indicated from spectral density analysis. Two major factors contribute the 1-min PM(2.5) cycles, i.e., the meteorological factors and source effects. Both the relative humidity and dew point showed consistent variation with PM(2.5), but the wind speed showed inverse variations with PM(2.5). Furthermore, the spectral density analysis of the meteorological factors (4-5, 2-2.5, 1-1.5 days, 12, 6-8, 3 h) may partially explain the cycles of PM(2.5). As for the sources effects, it can be shown from the strong dust storm of April 16-18th, 2006. PM(2.5) constantly increased tens and even hundreds of times high concentration within a few minutes due to the intensity of the dust sources.