Automated Humidity Control System for Aerosol Light Scattering Measurements

Atmospheric aerosols impact climate by scattering sunlight and acting as cloud condensation nuclei, with their scattering properties influenced by size, composition, and humidity. Measuring the relative humidity (RH) dependence of aerosol scattering is crucial for climate models, yet long-term data remain scarce. This research enhances the humidification system for measuring the aerosol light scattering humidity enhancement factor f(RH) at AppalAIR. Laboratory tests and modeling improved the control and reliability of expanded polytetrafluoroethylene membranes for regulating RH, a first-of-its-kind characterization. A compact ultrasonic humidifier was tested but proved unsuitable due to droplet interference. A new membrane-based humidifier was designed, tested, and deployed, improving measurement reliability. Enhanced control strategies outperformed microcontroller-based alternatives. The system successfully provided f(RH) data during a two-month field campaign and remains in use for long-term monitoring, with future work focused on refining controls and exploring new designs.<p></p>