When the atmospheric temperature is 0 °C, a vibrating rod mounted on a hot air balloon generates longitudinal waves traveling at a speed of 331 m/s. The vibrating rod's frequency is 1000 Hz. The hot air balloon rises in the sky. At a height where the temperature is T, the waves have a wavelength of 0.28 m. To obtain this wavelength, what should be the atmospheric temperature? Consider air as an ideal gas.