What is the specific gravity of dry air?

The specific gravity of dry air is indeed 1, which is commonly referred to as the standard reference for gases. Specific gravity compares the density of a substance to the density of a reference substance, typically water for liquids and solids, and air for gases. In the case of dry air, it is used as a benchmark against itself.

When defining specific gravity for air, it's based on the density of air, which is approximately 1.225 kg/m^3 at sea level and at 15°C, compared to the density of air at standard conditions, which is set at 1. This means that dry air does not float in lighter gases like helium or hydrogen and will stay suspended or rise when compared to heavier gases, which have a specific gravity greater than 1.

Understanding that specific gravity is a dimensionless quantity allows clarity in comparing the buoyancy and behavior of different gases under various conditions. Since the question specifies dry air and uses standard conditions, choosing a specific gravity of 1 accurately reflects this established relationship in the study of meteorology and atmospheric science.