Property Of Black Carbon Concentration And Source Analysis Over Urban And Suburban Of Lanzhou

The variation of black carbon (BC) concentration over urban and suburban areas of Lanzhou were analyzed using the BC observation data from the Semi-arid Climate and Environment Observatory of Lanzhou University (SACOL) from September2010to August2011. Then the backward trajectory of high altitude air over urban and suburban areas of Lanzhou were analyzed using HYSPLIT-4backward trajectory model. The main results are as follows.(1) The average BC concentration in urban area was much higher than that in suburban area with the values of5580and2270ng/m3respectively. The diurnal variation showed a bimodal distribution with the maximum value at08:00-10:00(Beijing Time), and the minimum around16:00in four seasons, the moments of the first peak BC concentration were later in autumn and winter than that in spring and summer. The annual variations of monthly maximum frequency BC concentration in urban and suburban areas were similar, the minimums of BC were shown in May with the values of2020and923ng/m3respectively, and the maximums were in January with their values of10230and4320ng/m3respectively. The values of maximum frequency monthly BC concentrations in urban area were higher than that in suburban area in November、December and January, and lower in other months throughout the year. The weekly variation was more obviously in urban area than that in suburban area, the values of BC concentration on working days were significantly higher than that on weekend in urban area in the heating period while little difference in the non heating period; but the values of BC concentration on working days were similar to that on weekend in the whole year in suburban area.The values of BC concentration were significantly decreased under the conditions of rain and snow event, and BC concentration under the condition of dust event was lower than the daily average concentration in the same month.(2) The annual maximum frequency BC concentration in urban area was far greater than that in suburban area with the values of3518and1465ng/m3respectively. The source of BC was mainly from local emission in urban area, but in suburban area mainly from surrounding area and background concentration respectively. The results showed that high altitude air mass was from clean areas in the southeast and southern when the BC concentration was low but from heavy industry area in the northwest when the BC concentration was high in urban areas;high altitude air mass was from clean area in the southeast when the BC concentration was low but from urban area in the northwest when the BC concentration was high in suburban area.