Which tool is used to measure the amount of water vapor in the air?

The tool used to measure the amount of water vapor in the air is the hygrometer. This instrument is specifically designed to quantify humidity, which is the concentration of water vapor present in the atmosphere. Hygrometers can come in various forms, such as digital hygrometers that use electrical components or analog hygrometers that often use materials that change properties with moisture content.

A psychrometer, while involved in measuring humidity, operates on a different principle. It uses two thermometers, one with a wet bulb and one with a dry bulb, to determine the relative humidity by comparing the temperatures.

A barometer measures atmospheric pressure, which is essential for weather forecasting but does not provide data on humidity levels directly.

A thermometer is utilized to measure temperature, which, while it can offer some insights for understanding weather, does not tell us anything about humidity or water vapor content. Therefore, the hygrometer is the most accurate and dedicated instrument for assessing the amount of water vapor in the air.