dalton preciptation law
Answers
Dalton's law (also called Dalton's law of partial pressures) states that in a mixture of non-reacting gases, the total pressure exerted is equal to the sum of the partial pressures of the individual gases.[1] This empirical law was observed by John Dalton in 1801 and published in 1802.[2] and is related to the ideal gas laws.
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➡️/Precipitation
gravity concentrates the atmospheric gases near the surface, at 5.5km, atmospheric pressure half that at the surface
90% of water vapor content is confined to the lower 6km
air rising -> expansion -> adiabatical (=no heat exchange with environment) cooling -> condensation
condensation and precipitation
at T>0oC: warm cloud process: condensation, gradual growth of water droplets by condensation and coalescence
at T<0oC: cold cloud process: involves also the formation and growth of ice crystals
two extra factors are needed to form precipitation:
sufficient moisture supply
sufficient vertical motion
warm cloud process
a moisture laiden air parcel rises, cools at dry adiabatic lapse rate (~1oC/100m) until it reaches the dewpoint, at which point condensation occurs. After that, any further rise causes cooling at the moist adiabatic lapse rate (0.5 - 0.9oC/100m), because of the released latent heat. (Fig)
super saturation: relative humidity > 100%
condensation nuclei are needed to increase condensation
most efficient particles: Aitken nuclei (0.01-0.1 micro m)
typical source: dust from land, sea spray (hygroscopic!)
5 million/l over land, 1 million/l over the ocean
experiment: salt crystals as condensation nuclei (Fig)
experiment: when a beer bottle is opened, a cloud forms in the neck. If temp. of the bottle is 5oC, temperature drops to ~-36oC when bottle is opened (Fig)
experiment: when beer is poored into a glass, bubbles form on scratches and dust particles, adding salt can increase the bubble formation: clouds in a glass of beer
excercise: condensation on a mirror in the bathroom (Fig); condensation on windshields
condensation only creates droplets < 100 micro m radius, while raindrops are of the order of 1mm
clouds are continuously forming and dissipating