Dilutions Over Treated Fields

Ryan D. SullivanDavid A. SullivanSullivan Environmental1900 Elkin Street, Suite 200Alexandria, VA 22308 1

Bystander Exposures Affected by 2 Fluxes: pesticide flux and heat flux (dilution potential)

• Conc. = emission x dilution

• Emission flux of pesticides has been focus

• Heat flux modification by tarped surfaces during critical nocturnal periods equally important

• 3 field studies in 2015 included off-field & on-field comparative heat flux and turbulent intensity data - - basis to refine dilution term

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Total Benefits of Tarps Should Be Considered

• Retention of A.I. and daughter products is very important

• But the full tarp benefits need to also consider the influence on mitigating worst-case dilution conditions (nocturnal inversions)

• Differences between neutral and inversion stability can be on the order of a 3x factor - - all else being equal

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Why Do Some Applications Eliminate Atmospheric Inversions Over the Field?

• Pre-application irrigation increases:• Thermal conductivity = greater downward heat

storages• Heat capacity• Heat reservoir

• Tarped applications promote heat storage by minimizing loss of heat by surface evaporation

• Black tarp also reduces loss of heat by reflected loss 4

Example of Tarp Covered Surface

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Non-Agricultural Example of Heat Island Effect

Example: shopping mall monitored by Sullivan Environmental with warm asphalt/concrete surfaces surrounded by grassy residential areas and wooded areas. During this period with very light wind speeds, counter flow was observed with the low-level flow of the colder converging air moving uphill, rather than the more common cold air drainage. The nocturnal surface temperature differential between the mall surface and the natural grass covered surfaces in this example was 8 to 10 C. In this sense, a heat island is an “island” of warm air surrounded by cooler air, i.e. an “oasis” in reverse.

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Example of Heat Island Caused by Warmer Surface Surrounded by Cooler Surfaces

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Surface Temperature at 11:13 P.M. hours on 4/26/2013

Wind flow from 160 degrees

(uphill in opposition to gravity flow)

Asphalt surface 15-18 F warmer than natural surfaces Grassy surface

Latest Field Data: Supports Refinement of Modeling for Ag Applications

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Key Factors to Atmos. Stability• Tarp color• Irrigated vs. unirrigated• Soil type

Difference between neutral and stable conditions

Blacktarp

Unirrigatedground

Whitetarp

Off-field Minus On-field Temperature Differences

Study Temperature Difference

(F) comment

bedded, black Tarp Florida June 2015 -6

IR Thermometer, Sfc Based

bedded, white tarp, California, Sept 2015 -0.2

measured 1m above surfaces

bare ground, California, October 2015 +1.2

measured 1m above surfaces

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Phasing In Of Comparative Heat Flux and Turbulence Data

On-Field Prepared Ground VersusBare ground natural surface

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Co-Variance Monitoring(sensible heat, water vapor, turbulent intensity)

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Bedded Black Tarp: 70 % Increase in Dilution Rates Over Treated Field

Day NightPeriod Wind Directions On-Field Off-Field On-Field Off-Field n n

6/15/15 1700 - 6/19/15 0046 all 0.16 0.15 0.165 0.118 2521 22666/15/15 1700 - 6/18/15 1500 20-160 0.155 0.154 0.173 0.125 1583 10486/15/15 1700 - 6/18/15 1500 340-360 0.167 0.156 0.172 0.096 163 1596/15/15 1700 - 6/18/15 1500 0-20 0.164 0.144 0.183 0.112 265 1956/18/15 1600 - 6/19/15 0046 20-160 0.128 0.137 0.146 0.135 67 169

weighted average 0-20 & 340-360 → 0.165 0.149 0.178 0.1056/15/15 1700 - 6/18/15 1500

Daytime Nighttime

12~70 percent increase in relative dilution over treated field

Vertical Dispersion Differences On-Field Versus Off-Field (bare ground)

10/17/2015 10/19/2015 10/21/2015 10/23/2015 10/25/2015 10/27/20150

0.05

0.1

0.15

0.2

0.25

0.3

0

0.5

1

1.5

2

2.5

3

3.5

Study SEC 2015A: Sigma Phi On-field and Off-field Compared with Wind Speed

on_Sig_Phi on_Sig_Phi Off_Sig_Phi Off_Sig_Phi

Sig

ma

phi

Win

d Sp

eed

(MPS

)

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On-Field Sensible vs Latent Heat Flux Bare Ground Application

10/17/2015 10/19/2015 10/21/2015 10/23/2015 10/25/2015 10/27/2015-30

20

70

120

170

Study SEC2015A: Sensible and Latent Heat Flux On Applied Field

ONFIELD Hs W/m^2 Smp LE_kh_wpl W/m^2 Smp

W/m

^2 S

mp

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Latest Field Data: Supports Refinement of Modeling for Ag Applications: On-field and Comparative Off-Field Data Collection

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Covariance Heat Flux

Krypton HygrometerLatent heat flux

Wind and temp.profile

Real timeAir density

Other Advancements in Flux Study Research

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Advanced GIS processing of fetch(Sub-meter accuracy 360 degree directions)

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Conclusions• Realistic assessment of nocturnal bystander exposures needs

to consider applied surface / tarp influence on dilution

• Currently modeling moderate dilution (neutral) at night as though extremely limited dispersion (stable inversion conditions)

• Near-field issue - - if >>100 m buffer zones using standard modeling methods - - expect minor differences

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Conclusions (Cont.)

• Potential future supplemental data for our flux studies to maximize downstream benefits of emissions studies:

• Dual co-variance monitoring of sensible and latent heat flux

• Flux plates to measure soil heat flux

• Net radiation measurements

• Support needed to fully delineate atmospheric dilution differences - - meteorological research separate from flux studies

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