The element composition of atmospheric particles at Beijing during Asian dust events in spring

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1 The element composition of atmospheric particles at Beijing during Asian dust events in spring Renjian Zhang, Zhenxing Shen, Tiaotao Cheng, Meigen Zhang, Yanju Liu Yunfei Wu Institute of Atmospheric Physics Chinese Academy of Sciences

2 Contents Significance of this study Observations and methods Results and Discussion Mass concentrations of chemical elements Soil mass concentrations Enrichment factor of chemical elements Concentration of local and non-local sources to Beijing mineral dust Conclusions

3 Significance of this study Mineral dust is one of the largest contributors to the global aerosol loading and has strong impacts on regional and global climates (Tegen et al., 1996; Wu et al., 2006), long-term climate trends (Petit et al., 1990, 1999), as well as marine and terrestrial ecosystems (Martin et al., 1988; Chadwick et al., 1999). Beijing is one of megacities in the world who confront severe challenges of air quality management and the features of air pollution in Beijing are changing from typical coal-combusion pollution to a compound pollution case (Zhang et al., 2003). In springtime, dust storms and local re-suspended dust due to traffic, and construction work enhance the complexity of particulate matter in Beijing (Guo et al., 2004) Up to now, only a few measurements of aerosol mass concentration, size distribution, chemical composition, or optical properties were performed in Beijing during dust events (Bergin et al., 2001; Hu et al., 2002; Duan et al., 2004; Wehner et al., 2004; Zhang et al., 2004, 2008)

4 oxidation of gaseous material, such as SO X and NO X occurs on the surface of mineral dust particles (Denterner et al., 1996) dust transport local re-suspended dust due to traffic and construction work complexity of particulate matter in Beijing dust particles change their size, shape and surface conditions dust particles mix internally with sulphate and anthropogenic contaminants through coagulation process (Roth and Okada, 1998; Wurzler et al., 2000) both the radiative properties of dust aerosols and their ability to be a cloud condensation nucleus are changed (Sokolik et al., 2001)

5 Observations and methods Observation time: the spring of 2004 Dust events: 9-11 March and March Non-dust events Observation site: Observation site: at the top of a two-floor building (8 meter high above the ground) which was located in the Institute of Atmospheric Physics, Chinese Academy of Sciences (39 58 N, E), near the fourth ring road, about 10 km north away from the centre of Beijing

6 observation site

7 Sampling: an eight-stage cascade impactor in a typical flow rate of 1.1 L min -1 (PIXE International Corp.) <0.25, , , , , , , and >16.0 Chemical element composition analysis: Proton Induced X-Ray Emission (PIXE) technique 20 elements: Al, As, Br, Ca, Cl, Cr, Cu, Fe, K, Mg, Mn, Ni, P, Pb, S, Se, Si, Ti, V and Zn

8 Proton Induced X-ray Emission (PIXE) Cascade Sampler (PIXE Corp.)

9 Results and Discussion 1.Mass concentrations of chemical elements Mass concentration (ug m -3 ) μg m -3 Dusty days Non-dusty days The mean mass concentrations of above 20 elements in all the particle samples collected during dust events were larger than those during nondusty period mineral 10-2 Mg Al Si P S Cl K Ca Ti V Cr Mn Fe Ni Cu Zn As Se Br Pb Chemical element Typical pollutant

10 Table 1 Elements Ratio between dusty days and non-dusty days and its mass percentage in total 20-element concentrations (pert1 and pert2 refers for dusty and non-dusty days) Element Ratio Pert1 (%) Pert2 (%) Pert1/Pert2 Element Ratio Pert1 (%) Pert2 (%) Pert1/Pert2 Mg Al Si K Ca Ti V Cr Mn Fe P S Cl Cu Zn As Se Br Pb Ni

11 bimodal Mass concentration (ug m -3 ) Mg Al Si Ca Fe Dusty Mg Al Si Ca Fe Non-dusty Mass concentration (ug m -3 ) S Cl Cu Zn Pb Dusty S Cl Cu Zn Pb Non-dusty Particle size D p (um) Particle size D p (um) Mean concentrations of dust and pollutant elements in size-segregated particle samples during dusty and non-dusty days.

12 Table 2 Mean percentages for major mineral and pollutant elements in fine (Dp< 0.25 µm), moderate (0.25 < Dp< 2.0 µm) and coarse (Dp > 2.0 µm) particles during dusty and non-dusty days. Element Sampling C (%) C (%) C 2.0- (%) Sampling C (%) C (%) C 2.0- (%) Al Mg Si K Ti Fe Ca Zn Cl S Pb Cu Dusty day Non-dusty day

13 2. Soil mass concentrations 300 C soil = 2.2 C Al C Si C Ca C Fe C Ti Malm et al., 1994 D p < 0.25 um Soil mass concentration (ug m -3 ) < D p < 2 um D p > 2 um dust storm coming dust, but not serious M-52: 28 February 08:20 28 Feb. 11:00 H-9: 9 March 20:30-10 March 8:30 H-10: 10 March 8:30-10 March 17:30 H-11: 10 March 17:30-11 March 8:30 H-12: 28 March 8:30 28 March 17:30 H-7: 29 March 8:00 29 March 14:00 H-8: 29 March 14:20 29 March 18:00 H-17: 29 March 18:00 30 March 8:00 H-18: 30 March 8:00 30 March 18:00 0 M-52 H-9 H-10 H-11 H-12 H-7 H-8 H-17 H-18 Sample number Size distribution of Soil dust during dusty and non-dusty days

14 3. Enrichment factor of chemical elements EF = (C x /C r ) a / (C x /C r ) c C x, C r are the concentrations of X element and reference element respectively, the subscript a refers to aerosol particles in the atmosphere, while c refers to a reference material. In this study, mineral element Al was used as the reference element in EF calculations

15 Enrichment factor Mg Si K Ti Fe Mn V Ca Cr Ni Zn Cl S Pb Cu As Br Se Chemical element Enrichment factors of elements referred to crust dust in total size particle samples.

16 Table 3 Enrichment factors referred to crust for major mineral and pollutant elements in fine (Dp< 0.25 µm), moderate (0.25 < Dp< 2.0 µm) and coarse (Dp > 2.0 µm) particles during dusty and non-dusty days. Element Sampling EF EF EF 2.0- Sampling EF EF EF 2.0- Al Mg Si K Ti Fe Ca Zn Cl S Pb Cu Dusty day Non-dusty day

17 Dusty D p < 0.25 um 10 4 Non-dusty D p < 0.25 um Enrichment factor Mg K Ca Ti Mn Fe Cu Zn Pb 10-1 Mg K Ca Ti Mn Fe Cu Zn Pb Element Element Enrichment factors of dust and pollutant elements referred to crust (cross), Mongolian sandy soil (triangle), Chinese soil (circle) and Chinese loess (square) in fine particles (D p <0.25μm) during dusty and non-dusty days.

18 Dusty 0.25 < D p < 2 um Non-dusty 0.25 < D p < 2um Enrichment factor Mg K Ca Ti Mn Fe Cu Zn Pb 10-1 Mg K Ca Ti Mn Fe Cu Zn Pb Element Element Enrichment factors of dust and pollutant elements referred to crust (cross), Mongolian sandy soil (triangle), Chinese soil (circle) and Chinese loess (square) in moderate particles (0.25μm <D p <2.0μm) during dusty and non-dusty days.

19 10 3 Dusty D p > 2 um 10 3 Non-dusty D p > 2 um Enrichment factor Mg K Ca Ti Mn Fe Cu Zn Pb Element Mg K Ca Ti Mn Fe Cu Zn Pb Element Enrichment factors of dust and pollutant elements referred to crust (cross), Mongolian sandy soil (triangle), Chinese soil (circle) and Chinese loess (square) in coarse particles (D p >2.0μm) during dusty and non-dusty days.

20 4. Contribution of local and non-local sources to Beijing mineral dust (Mg/Al) aerosol = m (Mg/Al) local + n (Mg/Al) non-local m + n=1 Sun et al., 2004 (Mg/Al)aerosol: Average ratio of Mg/Al in aerosol, (Mg/Al)local: Average ratio of Mg/Al in local soil sample (in this case, the value of 0.46 was used (Zhou et al., 2007)) (Mg/Al)non-local: Average ratio of Mg/Al in non-local soil sample (in this case, the value of 0.12 was used in Duolun desert (Sun et al., 2004))

21 The aerosol from outside Beijing accounted for 66.3% and 88.6% to the total mineral aerosol during dust evnet on March and March As during dust period in spring in Beijing, more frequent and stronger north or northwest wind bring much more dust particles from outside Beijing and result in the much greater contributions of non-local sources to aerosols in Beijing.

22 Conclusions During dust events most of chemical elements in particles were enhanced in mass concentration. Mineral elements exhibited a predominance in the sums of total element loadings either dusty or non-dusty days. Mineral elements in particles were mainly originated from crustal material, and typical pollutant elements were from anthropogenic pollution emissions Mineral dust particles were most possibly originated from the Mongolian sand soils and the Chinese loess in the spring of 2004 Aerosol from outside Beijing accounted for 66.3% and 88.6% to the total mineral aerosol during dust event on March and March 2004, respectively.

We greatly appreciated the reviewer for the insight comments and suggestions for

Responses to Anonymous Referee #2 We greatly appreciated the reviewer for the insight comments and suggestions for improving the quality of this manuscript. Below, we have addressed your concerns and provided