Upward fluxes of particles over forests: when, where, why?

Pryor, Sara C.; Barthelmie, R.J.; Sørensen, L. L.; Larsen, Søren Ejling; Sempreviva, A. M.; Grönholm, Tiia; Rannik, Ü.; Kulmala, M.; Vesala, Timo

doi:10.3402/tellusb.v60i3.16931

Cited by 13 publications

(18 citation statements)

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“…However, this simple model generally supports the conclusions of Nilsson et al (2001) and Pryor et al (2008a), who suggested that observed upward fluxes are due to the entrainment of particle-depleted, chemically-aged air from the free troposphere, which would result in a decrease in concentration (negative storage flux). This is also supported by a comparison of the median fluxes during decreasing mean diameter (F 18−452 = 1.3 × 10 6 m −2 s −1 ) and increasing mean diameter (F 18−452 = 2.3 × 10 6 m −2 s −1 ), since the mixing of chemically-aged air from above should result in an increasing mean diameter, which is associated with a higher upward flux.…”

Section: Mixingsupporting

confidence: 65%

“…Previous suggestions for upward fluxes included sources of particles within or close to the canopy top (Buzorius et al, 1998), or the entrainment of clean, particle depleted air from above (Pryor et al, 2008a). What is seen in this study combines both effects.…”

Section: Discussionmentioning

confidence: 48%

“…4.3, these upward fluxes are not associated with random, stochastic error, and remain even after filtering and corrections are applied. Pryor et al (2008a) investigated the effect of wind direction, assuming a point or line source of emissions, and the angle of attack on the sonic anemometer, which has been shown to give erroneous flux measurements. An investigation (not shown here) of fluxes sorted by wind direction and sonic angle of attack (as determined by the second sonic rotation angle) shows no correlation between flux direction and either variable (r 2 < 0.01).…”

Section: Discussionmentioning

confidence: 99%

“…Upward fluxes have been attributed to local emissions (Buzorious et al, 2000), particle re-suspension (Hicks et al, 1989), sources of particles within or close to the canopy top (Buzorius et al, 1998), stochastic effects in the data (Gaman et al, 2004), and entrainment during the growth of the mixing layer (Nilsson et al, 2001). Pryor et al (2008a) analysed data from two locations with the aim of determining the source of these upward fluxes. They found a possible causal link of upward fluxes to the entrainment of particle-depleted air from the free troposphere at one location.…”

Section: Introductionmentioning

confidence: 99%

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Aerosol flux measurements above a mixed forest at Borden, Ontario

et al. 2011

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Abstract. Aerosol fluxes were measured above a mixed forest by Eddy Covariance (EC) with a Fast Mobility Particle Sizer (FMPS) at the Borden Forest Research Station in Ontario, Canada between 13 July and 12 August 2009. Chemically speciated flux measurements were made at a height of 29 m at the same location between 19 July and 2 August, 2006 using a Quadrupole Aerosol Mass Spectrometer (Q-AMS). The Q-AMS measured an average sulphate deposition velocity of 0.3 mm s −1 and an average nitrate deposition velocity of 4.8 mm s −1 . The FMPS, mounted at a height of 33 m (approximately 10 m above the canopy top) and housed in a temperature controlled enclosure, measured sizeresolved particle concentrations from 3 to 410 nm diameter at a rate of 1 Hz. For the size range 18 < D < 452 nm, 60 % of fluxes were upward. The exchange velocity was between −0.5 and 2.0 mm s −1 , with median values near 0.5 mm s −1 for all sizes between 22 and 310 nm. The size distribution of the apparent production rate of particles at 33 m peaked at a diameter of 75 nm. Results indicate a decoupling of the above and below canopy spaces, whereby particles are stored in the canopy space at night, and are then diluted with cleaner air above during the day.

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Section: Mixingsupporting

confidence: 65%

Section: Discussionmentioning

confidence: 48%

Section: Discussionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Aerosol flux measurements above a mixed forest at Borden, Ontario

et al. 2011

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“…These percentages of net deposition fluxes are high even compared to aerosol deposition studies at boreal forest sites. Rannik et al (2003) observed 68% net deposition fluxes at a boreal forest site in Finland, and Pryor et al (2008) observed less than 60% net deposition fluxes over a forest in Denmark. Hence, due to the high percentage of net particle deposition fluxes in this study, together with the the results in Sect.…”

Section: Size-resolved Transfer Velocities For Particles In Thementioning

confidence: 99%

Emission and dry deposition of accumulation mode particles in the Amazon Basin

et al. 2010

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Abstract. Size-resolved vertical aerosol number fluxes of particles in the diameter range 0.25-2.5 µm were measured with the eddy covariance method from a 53 m high tower over the Amazon rain forest, 60 km NNW of Manaus, Brazil. This study focuses on data measured during the relatively clean wet season, but a shorter measurement period from the more polluted dry season is used as a comparison. Size-resolved net particle fluxes of the five lowest size bins, representing 0.25-0.45 µm in diameter, were in general dominated by deposition in more or less all wind sectors in the wet season. This is an indication that the source of primary biogenic aerosol particles may be small in this particle size range. Transfer velocities within this particle size range were observed to increase linearly with increasing friction velocity and increasing particle diameter.In the diameter range 0.5-2.5 µm, vertical particle fluxes were highly dependent on wind direction. In wind sectors where anthropogenic influence was low, net upward fluxes were observed. However, in wind sectors associated with higher anthropogenic influence, deposition fluxes dominated. The net upward fluxes were interpreted as a result of primary biogenic aerosol emission, but deposition of anthropogenic particles seems to have masked this emission in wind sectors with higher anthropogenic influence. The net emission fluxes were at maximum in the afternoon when the mixed layer is well developed, and were best correlated with horizontal wind speed according to the equationwhere F is the net emission number flux of 0.5-2.5 µm particles [m −2 s −1 ] and U is the horizontal wind speed [ms −1 ] at the top of the tower.

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The effects of leaf size and microroughness on the branch‐scale collection efficiency of ultrafine particles

et al. 2015

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Key Points:• UFP collection efficiency ( ) for four broadleaf species was measured• Rougher surfaces enhance ϵ even for hydraulically smooth flow • Longer leaf dimension has a thicker quasi-laminar boundary layer and smaller ϵ Abstract Wind tunnel experiments were performed to explore how leaf size and leaf microroughness impact the collection efficiency of ultrafine particles (UFP) at the branch scale. A porous media model previously used to characterize UFP deposition onto conifers (Pinus taeda and Juniperus chinensis) was employed to interpret these wind tunnel measurements for four different broadleaf species (Ilex cornuta, Quercus alba, Magnolia grandiflora, and Lonicera fragrantissima) and three wind speed (0.3-0.9 m s −1 ) conditions. Among the four broadleaf species considered, Ilex cornuta with its partially folded shape and sharp edges was the most efficient at collecting UFP followed by the other three flat-shaped broadleaf species. The findings here suggest that a connection must exist between UFP collection and leaf dimension and roughness. This connection is shown to be primarily due to the thickness of a quasi-laminar boundary layer pinned to the leaf surface assuming the flow over a leaf resembles that of a flat plate. A scaling analysis that utilizes a three-sublayer depositional model for a flat plate of finite size and roughness embedded within the quasi-laminar boundary layer illustrates these connections. The analysis shows that a longer leaf dimension allows for thicker quasi-laminar boundary layers to develop. A thicker quasi-laminar boundary layer depth in turn increases the overall resistance to UFP deposition due to an increase in the diffusional path length thereby reducing the leaf-scale UFP collection efficiency. It is suggested that the effects of leaf microroughness are less relevant to the UFP collection efficiency than are the leaf dimensions for the four broadleaf species explored here.

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Upward fluxes of particles over forests: when, where, why?

Cited by 13 publications

References 0 publications

Aerosol flux measurements above a mixed forest at Borden, Ontario

Aerosol flux measurements above a mixed forest at Borden, Ontario

Emission and dry deposition of accumulation mode particles in the Amazon Basin

The effects of leaf size and microroughness on the branch‐scale collection efficiency of ultrafine particles

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