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Dry deposition and spray drift of pesticides to nearby water bodies

Appendix F. Parameters necessary to calculate the drop temperature and the ventilation coefficient for water vapour

Latent heat of evaporation of water

The latent heat of evaporation of water L (J kg^-1)between –40° C and 40° C (J kg^-1) is given by:

where T_w is the water temperature (K).

Diffusivity of water vapour in air

The diffusivity of water vapour in air Dwa (m² s^-1) is given by (Pruppacher and Klett, 1997):

where:

T_w = water temperature (K)
P = pressure (atm)

Thermal conductivity of air

The thermal conductivity of moist air ka (J m^-1 s^-1 K^-1) is almost the same as the thermal conductivity of dry air. The thermal conductivity of dry air (J m^-1 s^-1 K^-1) is given by (Pruppacher and Klett, 1997):

where ta is the air temperature (C).

Saturation pressure of water vapour

The saturation pressure of water vapour above liquid water psat (N m^-2) between -

50 ° C and 50° C is given by (Pruppacher and Klett, 1997):

where:
a0 = 6.107799961× 10²
a1 = 4.436518521× 10¹
a2 = 1.428945805
a3 = 2.650648471× 10^-2
a4 = 3.031240396× 10^-4
a5 = 2.034080948× 10^-6
a6 = 6.136820929× 10^-9
tw = water temperature (C) 

Figure F-1. Saturation pressure of water vapour as a function of temperature.
Figur F-1. Vanddamps mætningstryk som funktion af temperatur.

References

Pruppacher, H.R., Klett, J.D. (1997) Microphysics of clouds and precipitation. Kluwer, Dordrecht, The Netherlands.

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