| 摘要: |
| 利用红外CO2监测仪对西安南郊3种人工植被不同高度下空气CO2浓度分别进行了3次昼夜观测，探讨了不同高度空气中CO2的浓度动态日变化规律及其影响因素。结果表明：西安南郊地区夏季一昼夜内空气中CO2浓度具有明显变化，从当日上午08:00到次日上午08:00，空气中CO2浓度变化呈现出由高变低再变高的规律，这种变化特点与昼夜温度变化基本一致，但两者在时间上并不完全同步。CO2浓度昼夜变化分为四个阶段，第一阶段在08:00 — 12:00，为CO2浓度较高阶段，平均浓度为516 μL ∙ L−1；第二阶段在13:00 — 21:00，为CO2浓度最低阶段，平均浓度为483 μL ∙ L−1；第三阶段在22:00到次日04:00，为CO2浓度较低阶段，平均浓度为502 μL ∙ −1；第四阶段在05:00 — 07:00，为CO2浓度最高阶段，平均浓度为533 μL ∙ L−1。在2 m高度范围内，空气中CO2浓度与高度呈负相关关系，与空气湿度呈正相关关系，风速对CO2昼夜浓度影响较小。白天光合作用强，空气对流作用强，空气中CO2浓度明显低于夜间。 |
| 关键词: 西安南郊 空气CO2浓度 昼夜变化阶段与规律 影响因素 人工植被 |
| DOI：10.7515/JEE201705010 |
| CSTR：32259.14.JEE201705010 |
| 分类号: |
| 基金项目:陕西师范大学大学生创新创业训练计划项目（201510718028）；黄土与第四纪地质国家重点实验室项目（SKLLQG1428） |
| 英文基金项目:National Undergraduate Training Programs for Innovation and Entrepreneurship of Shaanxi Normal University (201510718028); State Key Laboratory of Loess and Quaternary Geology (SKLLQG1428) |
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| Research on temporal and spatial variation of carbon dioxide concentration of summer air in southern suburbs of Xi’an |
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CHENG Jie, SONG Yi, LI Li, ZHOU Dianfang, ZHAO Jingbo
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1. College of Tourism and Environment, Shaanxi Normal University, Xi’an 710119, China
2. State Key Laboratory of Loess and Quaternary Geology, Institute of Earth Environment, Chinese Academy of Sciences, Xi’an 710061, China
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| Abstract: |
| Background, aim, and scope Whether the diurnal change and height change of urban air CO2 have natural change rules is a scientific problem deserved to be found out. About the insufficient change research on CO2 concentration of urban air in Xi’an, specifically there is little research on the diurnal change rule of CO2 concentration within 2 m height. Aiming at the deficiency, this paper develops the diurnal observation and research on CO2 concentration within 2 m height. The research purpose of the paper is to reveal the diurnal change of CO2 concentration of summer air in southern suburbs of Xi’an and the change within 2 m height; and scientific basis is provided to relieve the adverse effect of CO2. Materials and methods In order to make the research result have representativeness, the paper has selected three observation points in Yanta campus of Shaanxi Normal University in southern suburbs of Xi’an; and the three observation points are subjected to three times of diurnal observation from June 21 to June 22, from July 17 to July 18 and from July 21 to July 22 with clear weather. The observation point A is located in Peonies Garden majoring in peonies in the campus; the observation point B is located below the cedar forest; and the observation point C is located below the persimmon forest. The CO2 concentration of the air at 0.2 m, 1 m and 2 m height above the ground of the observation points is subjected to diurnal observation by infrared CO2 monitor; it is determined every one hour; and meanwhile, the air temperature, wind speed and humidity at 0.2 m, 1 m and 2 m height above the ground of the observation points are measured. Results The three times of diurnal observation results of three diurnal observation points show that the CO2 concentration change in southern suburbs of Xi’an is divided into four stages. The first stage from July 21 to July 22 is from 08:00 to 12:00; the change range of CO2 concentration is 480 — 510 μL ∙ L−1; the average concentration is 492 μL ∙ L−1; and it is the stage with higher CO2 concentration. The second stage is from 13:00 to 21:00; the change range of the CO2 concentration is 420 — 490 μL ∙ L−1; the average concentration is 466 μL ∙ L−1; and it is the stage with minimum CO2 concentration. The third stage is 22:00 — 04:00 of the next day; the change range of the CO2 concentration is 470 — 510 μL ∙ L−1; the average concentration is 488 μL ∙ L−1; and it is the stage with lower CO2 concentration. The fourth stage is 05:00 to 07:00; the change range of CO2 concentration is 520 — 570 μL ∙ L−1; the average concentration is 539 μL ∙ L−1; and it is the stage with maximum CO2 concentration. The diurnal change range of CO2 concentration at 0.2 m, 1 m and 2 m above the ground of A observation point from June 21 to June 22 is 420 — 550 μL ∙ L−1, 420 — 590 μL ∙ L−1 and 430 — 540 μL ∙ L−1; the average concentration is 492 μL ∙ L−1, 484 μL ∙ L−1 and 475 μL ∙ L−1. Along the increased height, CO2 concentration is reduced. CO2 change of other observation points within 2 m height is similar with the above conditions. Discussion Three times of diurnal observation results show that in the first stage from 08:00 to 12:00, the main reason of higher CO2 concentration in air is caused by the CO2 released by soil and accumulated CO2 generated by human activities in surface layer atmosphere; and it is decided by weak air convection and slow CO2 diffusion in this stage. In the second stage from 13:00 to 21:00, the reason of minimum CO2 concentration in air is caused by strong air turbulence effect in this stage; CO2 is reduced by convective diffusion concentration and the stronger plant photosynthesis in this stage can absorb SO2 in the air. In the third stage from 22:00 to 04:00, the reason of lower CO2 concentration in the air is caused by industrial production and weak production activities in this stage; and it generates little CO2. In the fourth stage from 05:00 to 07:00, the reason of maximum CO2 concentration in the air is that the air is in sinking stage; the CO2 relieved by soil is continuously accumulated so as to result in maximum CO2 concentration. The air temperature in south suburbs of Xi’an is in negative correlation with CO2 concentration; and it is caused by the increased photosynthesis of raised air temperature and air vertical convection diffusion. CO2 concentration within 2 m height is reduced along the increased height; and reason is that the lower part is close to the CO2 release source from the soil. CO2 concentration at night is higher than that in daylight, because the air humidity at night is greater than that in daylight; the weak air convection diffusion results in accumulated CO2 settlement in the air and CO2 concentration rises. Air humidity is in positive correlation with CO2 concentration content. Conclusions The diurnal change of CO2 concentration of three observation points in southern suburbs of Xi’an is divided into four stages. CO2 concentration change is in higher, minimum, lower and maximum change; and it reflects that low-level CO2 concentration diurnal change rule in city is controlled by the natural factors. Air CO2 concentration of A, B, C observation points is reduced along the increased height within 2 m height range; and it reflects that the change of low-level CO2 concentration in city is mainly controlled by natural factors. CO2 concentration in daylight is lower than that in night; and it is caused by the diffused CO2 in the air of CO2 absorbed by photosynthesis in the air and strong convection in daylight. CO2 concentration change in the air is in negative correlation with the air temperature; and it is caused by the increased air temperature, strong photosynthesis and high of air convection diffusion. The air humidity is in positive correlation with CO2 concentration; and the great air humidity is not beneficial to the convection diffusion. Recommendations and perspectives This paper develops the research on diurnal change of three plants and CO2 concentration within 2 m height range; and it needs to develop the observation research on more plants and greater height; the density of the height observation point must be increased on the height so as to obtain the ration relation between the height and CO2 concentration. In addition, the diurnal change of CO2 concentration in clear weather and height change of CO2 concentration has been researched in this paper; the CO2 concentration in cloudy days and haze days is different from the cloud day, so it needs to observe CO2 concentration change in cloudy days and haze days. |
| Key words: the south suburb of Xi’an CO2 concentration the diurnal variations influencing factors artificial vegetation |
