Saturday, August 31, 2019

Removal of methane from the atmosphere

https://en.wikipedia.org/wiki/Atmospheric_methane#Removal_processes says " Furthermore, in an attempt to absorb the methane that is already being produced from landfills, experiments in which nutrients were added to the soil to allow methanotrophs to thrive have been conducted. These nutrient supplemented landfills have been shown to act as a small scale methane sink, allowing the abundance of methanotrophs to sponge the methane from the air to use as energy, effectively reducing the landfill's emissions." Also says: "Forest soils act as good sinks for atmospheric methane because soils are optimally moist for methanotroph activity, and the movement of gases between soil and atmosphere (soil diffusivity) is high " So forests could be good.

Tuesday, August 20, 2019

Humidification for rain

This triangular cloth-covered framework device shown will deflect a huge volume of air into the almost saturated layer just above the sea during the course of a day and will facilitate the evaporation of spray above the surface by creating turbulence with the downwards direction of the air. Just before a sea breeze develops (breeze from sea to land) the air that is being warmed on land expands upwards and outwards, keeping the sea breeze from developing. Warm dry air from this expanded volume of air will be mixed, by this device, into the spray and almost-saturated air region just above the sea just before the sea breeze develops. A deeper moist layer will then blow in with the sea breeze, facilitating rain.
If the spray was just rising a few cm without the device and is forced a few m upwards by the wind with the device there will be a big increase in evaporation. If a few cubic km of air per day is directed down by the device you will have a huge amount of moist air. Imagine the device is 1 km long, 1/100 km high and wind blows at 10 km/hour for 20 hours. Then 2 cubic km of air per day could be forced down.
When there is a drought the land gets hotter because of no evaporation (hot deserts are hotter than tropical forests where there is evaporation). When land gets hotter the air above the land gets hotter and then relative humidity of the air drops and the vapour pressure deficit (VPD) increases a lot. From what I have read plants generally like a vapour pressure deficit (VPD) of between 0.8 kPa and 1.2 kPa. This means that the vapour pressure inside the plant minus the vapour pressure in the air should be 0.8 to 1.2 kPa. Failing this there is wilting, etc. Even if you do not get rain it might be worthwhile humidifying the air around the coast or planting more trees



Friday, August 16, 2019

Wetter or drier?

Will the world become wetter or drier overall? The article https://www.aaas.org/news/drying-atmosphere-spurs-decline-vegetation-growth says: "The findings reveal that atmospheric water vapor is expected to further wane throughout the 21st century due to rising air temperatures and a decline in the evaporation of the world's oceans."
People might find it strange that as air temperatures increase the evaporation from oceans decreases, but here is an explanation: When it comes to evaporation from the sea, most evaporation occurs when the sea is hotter than the air above it. With global warming the land heats up more than the sea and so you might tend to get air that is relatively hotter than the sea blowing to sea. When hotter air is above the sea the sea cools the air above and the relative humidity (RH) of this air increases and less evaporation results into the air because RH is higher. When The sea is warmer than the air above it the sea heats the air above it and the RH of the air decreases and more evaporation occurs because RH is low. When you have cold sea near to hot land you can get "negative evaporation" - the water vapour condenses out of the hot air above the cold sea and fog occurs.
One factor that could increase the evaporation is increased downwelling sky radiation from hotter air, but the effect of increasing RH of hotter air above cold water appears to be a clear winner in certain regions at present.

Solution: A stagnant saturated layer builds up just above the sea surface so a sheet along the coast and above the sea that deflects air downwards and gives turbulence could partially solve the problem and increase evaporation. Also see https://journals.ametsoc.org/doi/full/10.1175/JCLI3519.1 
I have been dealing with evaporation equations for a while and I take the average of 5 equations (equations from Fitzgerald, Rohwer, Engineering Toolbox, Horton, Meyer) and here are some results: Suppose wind speed is 10 km per hour, RH=80% above the sea, sea temperature is 18 deg C and atmospheric pressure is 760 mm of mercury.
If we increase the air temperature above the sea we get this. 

Tair= 0 deg C then evaporation is 13 mm per day. 
Tair=10 deg C then evaporation is 9 mm per day. 
Tair= 20 deg C then evaporation is 1 mm per day. 
Tair=30 deg C then fog forms above water.