It is the weight of the air itself that causes air pressure. Fluctuations occur due to changes in wind and temperature.We live in air pressure of about 15# per square inch.
i have no idea sorry
Changes in density (more or less water vapor), changes in temperature, tides (even air masses are affected Earth's rotation, the Moon and the Sun).
You asked the question wrong, a Thermometer is NOT to air pressure, a Barometer is to Air Pressure, a Thermometer is to Temperature. Because why? Well? Because a thermometer has the word mom in it to...