The effect of vegetative buffers on wind and dispersion of particulate matter around poultry barns

Transcription

1 The effect of vegetative buffers on wind and dispersion of particulate matter around poultry barns Andreas Christen (1), Daryll Pauls (2), Shabtai Bittman (3) (1) Department of Geography, University of British Columbia, Vancouver, BC, Canada (2) Atmospheric Science Program, University of British Columbia, Vancouver, BC, Canada (3) Agri-Food Canada, Agassiz, BC, Canada - Cross-border Air and Waste Solutions

2 Motivation Controlling emissions of particulate matter from poultry facilities is desirable to mitigate negative impacts on natural resources (air and water pollution), agricultural plots, animal and human health. Vegetative buffers can possibly filter emitted particulate matter and reduce total emissions leaving a property. Emissions from poultry barn visualized using PNWIS smoke 2011 Christen, (Photo: Pauls and A. Bittman Christen, / Nov 10, UBC) 2011

3 Density of facilities in the Lower Fraser Valley

4 Airflow of a typical 2-barn layout Air intake Exhaust Air intake

5 Without vegetative buffer Flow is accelerated between barns. The emitted particulate matter is quickly dispersed and carried away. With vegetative buffer Wind speed is slowed, mixing is reduced causing locally higher concentrations. High concentrations of particulate matter means higher probability of deposition on leaves and ground. However, boundary layer resistances are also higher, reducing deposition rates.

6 Research questions - What is the potential of vegetative buffers to remove particulate matter before it leaves a property? - What would be most efficient buffer layouts that promote the removal of particulate matter - arrangement, height and density?

7 Layout considerations for vegetative buffers In-fill of alleyway Perimeter Property line + Vegetation removes particulate matter where concentrations are highest, i.e. close to source. + Moderate costs and maintenance. - Complicates operation (access to alleyway) - Removes particulate matter downwind of facility, where concentrations are presumably lower. - Substantial costs and water need. + Acts also as noise and visibility barrier.

8 Methods - Numerical model runs using the microclimate model Envi-met (Version 3.1b5, Bruse 2010) - Envi-met is a 3-d Eulerian CFD model that is designed to simulate interactions between surfaces, buildings and plants, and the air flow which may contain particulate emissions (PM10). - Modelled domain: 180 x 120 x 30 grid cells at a grid resolution of 1.5 x 1.5 m horizontally.

9 Model runs Reference In-fill of alleyway Perimeter R Neutral stability 1.7 m/s wind at 1.5 m 6 x 2 PM10 sources of 10 mg s -1 on each side of alleyway at 1.5 m height + I1 2m tall staggered shrubs with a plan area density of 13% (300 m 3 vegetation) I2 Same as I1 with only 1/3 leaf area density (300 m 3 vegetation) I3 Same as I1 but 6m tall (900 m 3 vegetation) P1 6m tall coniferous hedge, 15m away from edges of barn (6,000 m 3 vegetation) P2 Same as P1 but 30m away (8,000 m 3 vegetation) P3 Same as P2 but 15m tall (24,000 m 3 vegetation)

10 Effect of perimeter buffer on wind speed (P1) Relative change in wind (vs. no buffer) Wind -50% -40% -30% -20% -10% 0 +10% 60 Cross-wind distance (m) Cavity behind hedge Along-wind distance (m) Acceleration in alleyway

11 Effect of in-fill buffer on wind speed (I1) Wind Relative change in wind (vs. no buffer) -50% -40% -30% -20% -10% 0 +10% 60 Cross-wind distance (m) Reduction of wind in alleyway Cavity behind hedge Along-wind distance (m)

12 Effect of buffers on wind speed Change in wind Change in wind +20% no change -20% -40% -60% % no change -20% -40% Hedge Alleyway Alleyway with infill Hedge -60% Along-wind distance (m) P1 I1 Wind

13 Modelling PM10 Concentrations Wind Concentrations (µg m -3 ) Cross-wind distance (m) x 6 Sources at 1.5 m height with 10 mg s Along-wind distance (m)

14 Effect of buffer on PM10 concentrations Change in PM10 concentration (µg m -3 ) 600 Hedge Alleyway Hedge Along-wind distance (m) P1 Change in PM10 concentration (µg m -3 ) Alleyway with infill Along-wind distance (m) I1 Wind

15 Change in PM10 concentration in alleyway 40% 38% Change to reference (R) 30% 20% 10% 0% -10% 26% 20% 2% 3% -1% I1 I2 I3 P1 P2 P3 Increase Decrease In-fill Perimeter In-fill

16 Effect of leaf area density In-fill only, average values in alleyway at 1.5 m above ground 2.0 1,000 Wind (m s -1 ) Concentration (µg m -3 ) Leaf area density (m 2 m -3 ) In-fill Leaf area density (m 2 m -3 ) In-fill

17 Total deposition of PM10 on ground, vegetation and roofs Reference Wind P1 6m hedge Deposition on leaves Wind Total PM10 deposition Less deposition in lee 0 50m µg m -2 s -1

18 PM10 removal by vegetation Fraction of total emissions removed by leaves % 8% 4% 3% 3% 2% I1 I2 I3 P1 P2 P3 In-fill Perimeter

19 800 Cross-wind integrated PM 10 deposition roofs 3% Wind PM 10 deposited (µg m 1 s 1 ) Vents ground 97% Scenario R (with no buffer) Along-wind distance (m)

20 800 Cross-wind integrated PM 10 deposition vegetation 9% Wind roofs 3% PM 10 deposited (µg m 1 s 1 ) Scenario P3 (15m high trees) Additional deposition on leaves ground 88% Less deposition on ground in cavity Hedge Along-wind distance (m)

21 Fraction of PM10 emitted that is removed before leaving the property Deposited on vegetation Deposited on roof Deposited on ground % 30% 8% 1% 14% 4% 1% 23% 9% 1% 14% 3% 1% 25% 2% 1% 26% 3% 1% 28% R I1 I2 I3 P1 P2 % of emitted PM 10 removed P3 No buffer Infill Perimeter

22 Summary - As expected, vegetative buffers decrease wind and consequently increase concentrations (desired). - Perimeter layouts show little to no impact. More efficient to modify wind and dispersion is an infill of the alleyway. - In the best case, up to ~10% of emitted PM10 was deposited on the buffer. - In none of the scenarios, total PM10 leaving the property was significantly reduced. In some cases the enhanced deposition on leaves was offset by much reduced deposition on ground behind buffer elements.