Weather, Atmosphere and Headaches
There are many ways in which the weather can cause headaches. There are direct weather effect; i.e., barometric pressure, thunderstorms and ionisation of the air. Furthermore, the amount of sunlight you get - whether too much or too little - can be surprisingly important. Finally, hot weather can dehydrate you, which can directly cause headaches.
Direct Weather Effects
Ions are atoms or molecules which have become electrically charged - either by the removal of one or more electrons (one of the atomic particles) which gives a positive ion, or by the addition of an electron (which gives a negative ion). Transfer of electrons like this is the basis for static electricity.
Are you one of those people who feel very oppressed when a thunderstorm is due? And afterwards, do you feel invigorated as the rain splashes down? If so, you may be sensitive to electrical charges. Before a thunderstorm, the air is heavily charged with positive ions, one of the two forms of static electricity. As the thunderstorm passes, the air changes from being positively charged to being negatively charged.
Typically, before a thunderstorm the hot, humid, oppressive, positively charged atmosphere makes certain people feel tense and on edge, and this edginess often manifests itself as headaches, which are relieved as the storm eventually passes over. If you're particularly sensitive to positive ions, and there's thunder in the air, try taking a shower. This can help for the same reasons that being near a fountain or a mountain stream can - sprays of water create negative ions, which will relieve your symptoms somewhat.
Offices and ions
Much the same thing occurs in offices, but on a smaller scale. Positive charges tend to build up because the insides of offices are usually dry, with the humidity artificially controlled down to a low level; and the petroleum-based materials from which office carpets, furniture and equipment are made encourage the build-up of static electricity. How many times have you walked across an office and felt a slight electric shock as your hand touched the door handle? This is static electricity building up on your body, often caused by the action of your synthetic-soled shoes on synthetic carpets.
Sometimes the static in an office fills the air with positive ions. Under these conditions the office feels oppressive and stuffy, and you may suffer constant headaches. You could counteract this feeling by opening the windows to let in some fresh air, but in offices with central air-conditioning, the windows are often sealed.
Devices called ionisers can sometimes help control this situation. These push out negatively ionised air to counteract and annihilate the positive ions floating around in the office air. However, ionisers are moderately expensive to buy, and are not necessarily going to make you feel much better. Do give them a trial run before you buy, to see whether they help you or not. (Ionisers may also help remove pollen and dust from the air, too.)
Barometric pressure
We often hear of old soldiers complaining that they feel their war wounds more when there's bad weather coming. Some arthritis sufferers also find that their joints are more painful when the air pressure is low.
The reason barometric pressure varies is simple enough. Water vapour, molecule for molecule, is lighter than the gases that make up the remainder of the atmosphere. Since water vapour displaces other gases from the air, damp air weighs less than dry air. 'Barometric pressure' measures the weight of the atmosphere pressing on the surface of the earth; so, in damp conditions barometric pressure is less, because the extra water displaces the gases in the air and makes the atmosphere above the measuring point that much lighter.
Quite why this should make joints more painful and war wounds more sensitive, no one knows. Is it the barometric pressure itself? Unlikely; it's probably the humidity of the atmosphere. Some people get headaches related to barometric-pressure, being worse in damp conditions and better in dry ones.
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