Abstract
Abstract. Composition and size distribution of atmospheric aerosols from Xi'an city (~400 m, altitude) in inland China during the spring of 2009 including a massive dust event on 24 April were measured and compared with a parallel measurement at the summit (2060 m, altitude) of Mt. Hua, an alpine site nearby Xi'an. EC (elemental carbon), OC (organic carbon) and major ions in the city were 2–22 times higher than those on the mountaintop during the whole sampling period. Compared to that in the non-dust period a sharp increase in OC was observed at both sites during the dust period, which was mainly caused by an input of biogenic organics from the Gobi desert. However, adsorption/heterogeneous reaction of gaseous organics with dust was another important source of OC in the urban, contributing 22% of OC in the dust event. In contrast to the mountain atmosphere where fine particles were less acidic when dust was present, the urban fine particles became more acidic in the dust event than in the non-dust event, mainly due to enhanced heterogeneous formation of nitrate and diluted NH3. Cl− and NO3− in the urban air during the dust event significantly shifted toward coarse particles. Such redistributions were further pronounced on the mountaintop when dust was present, resulting in both ions almost entirely staying in coarse particles. On the contrary, no significant spatial difference in size distribution of SO42− was found between the urban ground surface and the mountain atmosphere, which dominated in the fine mode (<2.1 μm) during the nonevent and comparably distributed in the fine (<2.1 μm) and coarse (>2.1 μm) modes during the dust event.
Highlights
Dust is a major source of particulate matter to the atmosphere
The current study demonstrated that dyr2u==s10.t.2909sx t-o0.r83m has different effects o0.n1 the chemical properties of aerosols from the ground surfac0e.1 (∼ 4001m a.s.l.)10and the10m0 ounta1i0n00top troposphere (2060 m a.s.l.)C, ornecseunltrtaitniogn iinnPaMc10id, μitgymo-3f fine particles increasing on the urban ground surface and decreasing in the mountFaigiunrteo2p. aInttmercoosmpphareisroen wof hcoemnpodnuesnttswmaeassuprreedsbeyntht.e 9-stage sampler and the PM10 sampler during the campaign
Tai have been measured to recognize the horizontal differences in aerosol chemistry besample was collected on a day/night basis at an airflow rate of 100 L min−1, while the size-segregated samples were collected for 4 days in each set at an airflow rate of 28 L min−1 tween the two mountain areas (Wang et al, 2011c, 2012b). with 9 size bins as < 0.4, 0.4–0.7, 0.7–1.1, 1.1–2.1, 2.1–3.3, We found Gobi desert plant is the major source of organic 3.3–4.7, 4.7–5.8, 5.8–9.0 and > 9.0 μm, respectively
Summary
Dust is a major source of particulate matter to the atmosphere. Global annual mean burden of aerosol dust is about 20 Tg (± 40 %) (McNaughton et al, 2009). East coastal China (see Fig. 1 for the locations), to 2.1 Collection of PM10 and size-segregated particles identify the similarity and difference in chemical composition and size distribution of aerosols between the ground sur- Xi’an city is situated in Guanzhong Basin, a semi-arid region face and the free troposphere (Wang et al, 2011c, 2012b). (organic carbon), inorganic ions and organic compounds in PM10 of Mt. Hua and Mt. Tai have been measured to recognize the horizontal differences in aerosol chemistry besample was collected on a day/night basis at an airflow rate of 100 L min−1, while the size-segregated samples were collected for 4 days in each set at an airflow rate of 28 L min−1 tween the two mountain areas (Wang et al, 2011c, 2012b). The PM10 sampling duration was changed into 3–6 h depending on the particle loading, while the size-segregated sampling duration was changed into one day
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