西安市混合功能区冬夏季大气颗粒物中可溶性Fe的分布特征

唐卓悦; 卢迪; 沈振兴; 雷亚莉

doi:10.7524/j.issn.0254-6108.2020072704

西安交通大学能源与动力工程学院环境科学与工程系，西安，710049

通讯作者: E-mail：zxshen@mail.xjtu.edu.cn;

基金项目:

国家自然科学基金（41877383）资助

Characteristics of soluble Fe in atmospheric particles during winter and summer in an urban mixed-use area in Xi'an

Department of Environmental Science and Engineering, Xi’an Jiaotong University, Xi’an , 710049, China

Corresponding author: SHEN Zhenxing, zxshen@mail.xjtu.edu.cn ;

Fund Project: the National Natural Science Foundation of China (41877383)

摘要: 可溶性铁（Fe)一方面作为营养元素影响着生物地球化学循环，另一方面作为氧化剂对大气二次气溶胶的形成也有重要影响。本文分别开展了西安市混合功能区冬夏季不同粒径大气颗粒物的观测研究，通过使用改良的液体波导毛细管池（LWCC）测定颗粒物中酸性介质提取的可溶性铁浓度，并探究其季节变化、昼夜分布及粒径分布特征。季节分布特征表明,可溶性Fe(Ⅱ)浓度冬季高于夏季，而可溶性Fe(Ⅲ)浓度则夏季高于冬季。不同价态的可溶性Fe的季节分布特征差异明显，白天PM_2.5中可溶性Fe(Ⅱ)和总可溶性性Fe的质量浓度和溶解度都大于夜晚的PM_2.5样品，Fe(Ⅲ)则白天与夜晚无明显区别。粒径分布结果表明,溶解性Fe主要分布在细颗粒物中，且大气颗粒物的粒径越小，Fe(Ⅱ)_sol与Fe(Ⅱ)_total之比的变化范围越大，可溶性Fe(Ⅱ)和Fe(Ⅲ)之间的转化更为活跃。

Abstract: Soluble Fe influenced on the Biogeochemical cycle and the secondary aerosol formation. In this study, diurnal, seasonal variation and size distribution of soluble Fe in atmospheric aerosols were investigated in an urban mixed-use area site in Xi’an. In this paper, we have carried out observational studies of atmospheric particulates with different particle sizes in an urban mixed-use area site of Xi’an in winter and summer. By using an improved liquid waveguide capillary cell (LWCC) to determine the concentration of soluble iron extracted from the acidic medium in the particulates, and to explore its seasonal changes, day and night distribution and particle size distribution characteristics. The results show that the concentration of soluble Fe(Ⅱ) in winter was higher than that in summer, while for summer soluble Fe(Ⅲ) level was higher than that in winter. The mass concentration and solubility of soluble Fe(Ⅱ) and total soluble Fe in PM_2.5 during daytime were found to be greater than those during nighttime. However, Fe(Ⅲ) showed no obvious difference between day and night. The size distribution results showed more active conversion between Fe(Ⅱ) and Fe(Ⅲ) at smaller particle size, which indicated that the conversion rate of Fe(Ⅱ) and Fe(Ⅲ) in PM_2.5 was higher than those in PM_2.5-₁₀ and PM₁₀.

Key words:

PM_2.5 /
Fe(Ⅱ) /
Fe(Ⅲ) /
size distribution

c(Fe(Ⅱ)_sol)/(ng·m^-3)

c(Fe(Ⅲ)_sol)/(ng·m⁻³)

c(Fe(Ⅱ)_total)/(ng·m⁻³)

溶解度/%

白天

38.8±9.5

12.7±9.7

52.4±12.0

73.3±9.9

夜晚

22.7±7.7

15.0±7.1

37.7±10.2

56.1±12.3

PM_2.5

PM_2.5−₁₀

PM₁₀

昼Fe(Ⅱ)_sol/(ng·m⁻³)

32.3±11.4

5.4±2.6

2.3±1.0

夜Fe(Ⅱ)_sol/(ng·m⁻³)

28.2±10.2

6.7±3.9

3.5±2.8

昼Fe(Ⅲ)_sol/(ng·m⁻³)

16.6±6.8

8.8±2.7

5.4±2.5

夜Fe(Ⅲ)_sol/(ng·m⁻³)

17.0±7.1

7.1±3.3

4.3±2.3

昼Fe溶解度/%

26.7±2.3

19.7±2.2

9.7±4.0

夜Fe溶解度/%

21.1±6.6

16.8±2.2

6.8±4.7

西安市混合功能区冬夏季大气颗粒物中可溶性Fe的分布特征

通讯作者: E-mail：zxshen@mail.xjtu.edu.cn;

西安交通大学能源与动力工程学院环境科学与工程系，西安，710049

收稿日期: 2020-07-27

录用日期: 2021-11-26

网络出版日期: 2022-01-05

基金项目:

国家自然科学基金（41877383）资助

关键词:

PM_2.5 /
Fe(Ⅱ) /
Fe(Ⅲ) /
粒径分布

Characteristics of soluble Fe in atmospheric particles during winter and summer in an urban mixed-use area in Xi'an

Corresponding author: SHEN Zhenxing, zxshen@mail.xjtu.edu.cn ;

Department of Environmental Science and Engineering, Xi’an Jiaotong University, Xi’an , 710049, China

Received Date: 2020-07-27

Accepted Date: 2021-11-26

Available Online: 2022-01-05

Fund Project: the National Natural Science Foundation of China (41877383)

Keywords:

PM_2.5 /
Fe(Ⅱ) /
Fe(Ⅲ) /
size distribution

全文HTML

铁（Fe）作为大气气溶胶中一种主要的微量元素^[1]，其通过促进水中浮游生物的光合、呼吸、固氮^[2]，从而影响碳的生物化学循环进而最终影响地球的气候^[3]。Fe来源广泛，包括自然源（如沙尘）和人为源（如交通排放、钢铁及其他工业活动等）^[4]。研究发现,全球大气Fe循环的95%以上来自于沙尘地区，而人为源气溶胶Fe含量仅占全球大气铁循环的5%。然而，人为源气溶胶中铁的溶解度远远大于沙尘气溶胶中铁的溶解度，尽管人为源气溶胶Fe含量较少，但其贡献的可溶性Fe超过50%^[5-6]。一方面，人为源气溶胶中的可溶性Fe由于具有生物可利用性进而对Fe的生物地球化学循环有重要意义；另一方面，溶解性铁对二次气溶胶的形成也有重要的作用，比如Fe(Ⅲ)具有较高的氧化性，可以通过催化与氧化反应将S(IV)转化为S(VI)^[7]， Fe(Ⅲ)也可与大气中的有机酸络合从而参与光化学反应^[8]。

西安地处关中平原中部，北有黄土高原，南有秦岭山脉，为典型的盆地地形，空气污染较为严重，开展该地区大气气溶胶中溶解性Fe的分布特征研究对于探究Fe的环境效应有着重要的作用。因此，本研究通过对西安市混合功能区大气颗粒物中不同化学形态Fe的浓度特征、昼夜分布、粒径分布及季节变化特征的研究，以期探究大气颗粒物中Fe的溶解度和氧化还原特征。

3. 结论( Conclusions )

本研究通过对比冬夏季PM_2.5中Fe特征发现，Fe(Ⅱ)_sol浓度冬季高于夏季，可能是由于冬季污染物水平较高，SO₂等还原性物质较多，Fe(Ⅲ)催化氧化成为硫酸盐等物质后被原为Fe(Ⅱ)。而Fe(Ⅲ)_sol浓度则正好相反，表现出夏季高于冬季的特征，夏季光照强度较强，臭氧浓度高，氧化性强，Fe(Ⅱ)光氧化为Fe(Ⅲ)。Fe(Ⅱ)_sol和Fe(Ⅲ)_sol含量浓度在昼夜变化、粒径变化中都表现出一定的分布特征。白天PM_2.5中Fe(Ⅱ)_sol和Fe(Ⅱ)_total的质量浓度和溶解度都大于夜晚的PM_2.5样品，可能是由于光照条件的改变，光照增强促进Fe(Ⅱ)_sol和Fe(Ⅱ)_total的溶出，但是Fe(Ⅲ)_sol没有展现出很强的昼夜变化特征。较粗的样品（2.5 — 10 µm）中，Fe(Ⅱ)_sol与Fe(Ⅱ)_total之比的变化范围略小一些，为17% — 60%，在粒径大于10 µm的粗粒子中Fe(Ⅱ)_sol与Fe(Ⅱ)_total之比的变化范围明显小了很多，为12% — 38%，PM_2.5样品中Fe(Ⅱ)_sol与Fe(Ⅱ)_total之比的变化最大，表明粒径越小，Fe(Ⅱ)和Fe(Ⅲ)之间的转化更为活跃。

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