Temperature is the measure of thermal or internal energy of the molecules within an object or gas. We can measure temperature of an object using either direct contact or remote sensing. Temperature of air is closely related to other atmospheric properties, such as pressure, volume and density.
Density measures the ‘heaviness’ of an object or how closely ‘packed’ the substance is. Density is related to both the type of material that an object is made of and how closely packed the material is.
Pressure is the force exerted over a given area or object, either because of gravity pulling on it or other motion the object has. Molecules in the air produce pressure through both their weight and movement, and this pressure is connected to other properties of the atmosphere.
Humidity is a measure of the amount of moisture in the air. It tells you how comfortable it is to be outside, and if there is enough moisture to create clouds and rain.