气候变化领域集成服务门户(CCPortal): Residence times of air in a mature forest: observational evidence from a free-air CO2 enrichment experiment

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DOI	10.5194/acp-23-2145-2023
	Residence times of air in a mature forest: observational evidence from a free-air CO2 enrichment experiment
	Bannister, Edward J.; Jesson, Mike; Harper, Nicholas J.; Hart, Kris M.; Curioni, Giulio; Cai, Xiaoming; MacKenzie, A. Rob
发表日期	2023
ISSN	1680-7316
EISSN	1680-7324
起始页码	2145
结束页码	2165
卷号	23 期号:3 页码:21
英文摘要	In forests, the residence time of air - the inverse of first-order exchange rates - influences in-canopy chemistry and the exchanges of momentum, energy, and mass with the surrounding atmosphere. Accurate estimates are needed for chemical investigations of reactive trace species, such as volatile organic compounds, some of whose chemical lifetimes are on the order of average residence times. However, very few observational residence-time estimates have been reported. Little is known about even the basic statistics of real-world residence times or how they are influenced by meteorological variables such as turbulence or atmospheric stability. Here, we report opportunistic investigations of residence time of air in a free-air carbon dioxide enrichment (FACE) facility in a mature, broadleaf deciduous forest with canopy height of h(c) asymptotic to 25 m. Using nearly 50 million FACE observations, we find that median daytime residence times in the tree crowns range from around 70 s when the trees are in leaf to just over 34 s when they are not. Residence times increase with increasing atmospheric stability, as does the spread around their central value. Residence times scale approximately with the reciprocal of the friction velocity, u(). During some calm evenings in the growing season, we observe distinctly different behaviour: pooled air being sporadically and unpredictably vented - evidenced by sustained increases in CO2 concentration - when intermittent turbulence penetrates the canopy. In these conditions, the concept of a residence time is less clearly defined. Parameterisations available in the literature underestimate turbulent exchange in the upper half of forest crowns and overestimate the frequency of long residence times. Robust parameterisations of residence times (or, equivalently, fractions of emissions escaping the canopy) may be generated from inverse-gamma distributions, with the parameters 1.4 <= alpha <= 1.8 and beta = h(c)/u() estimated from widely measured flow variables. In this case, the mean value for tau becomes formally defined as (tau) over bar = 0/(alpha -1). For species released in the canopy during the daytime, chemical transformations are unlikely unless the reaction timescale is on the order of a few minutes or less.
学科领域	Environmental Sciences; Meteorology & Atmospheric Sciences
语种	英语
WOS研究方向	Environmental Sciences & Ecology ; Meteorology & Atmospheric Sciences
WOS记录号	WOS:000933045600001
来源期刊	ATMOSPHERIC CHEMISTRY AND PHYSICS
文献类型	期刊论文
条目标识符	http://gcip.llas.ac.cn/handle/2XKMVOVA/273907
作者单位	University of Birmingham; University of Birmingham; University of Birmingham
推荐引用方式 GB/T 7714	Bannister, Edward J.,Jesson, Mike,Harper, Nicholas J.,et al. Residence times of air in a mature forest: observational evidence from a free-air CO2 enrichment experiment[J],2023,23(3):21.
APA	Bannister, Edward J..,Jesson, Mike.,Harper, Nicholas J..,Hart, Kris M..,Curioni, Giulio.,...&MacKenzie, A. Rob.(2023).Residence times of air in a mature forest: observational evidence from a free-air CO2 enrichment experiment.ATMOSPHERIC CHEMISTRY AND PHYSICS,23(3),21.
MLA	Bannister, Edward J.,et al."Residence times of air in a mature forest: observational evidence from a free-air CO2 enrichment experiment".ATMOSPHERIC CHEMISTRY AND PHYSICS 23.3(2023):21.