Technical Description


Instrumentation


Research Interests

HEC: Technical Description

The chamber consists of a constant temperature room (Luwa Environmental Specialties) of 2.5× 2.5 × 2.75 m³ that houses a flexible Teflon bag. A schematic diagram of the experimental setup is shown in the figure below.

The flexible bag inside the room has a volume of 5 m³ (1.7 × 1.7 × 1.7 m³). The bag is made from 2 mil PFA Teflon, which is a transparent and nonreactive material. The bag is suspended within the room by a stainless steel frame, which also supports the bottom of the bag and thereby provides a clearance of 0.3 m between the floor of the enclosure and the bag. Two manifolds having multiple ports are located on opposite sides of the bag.

The temperature of the room is controlled between 20 and 40ºC by using an internal conditioning plenum that distributes the conditioned air evenly across the ceiling. Temperature is measured within the bag by three thermocouples. One RTD sensor measures the temperature outside of the bag. Ultraviolet irradiation of the bag is provided by forty-eight 40-W Sylvania 350 BL blacklights affixed to the room walls. The walls, the ceiling, and the floor are covered by reflective aluminum sheets to maximize light intensity.

Under normal operation, the chamber is operated in a feedback-controlled dynamic mode (i.e., a steady-state volume), for which the inlet flow equals the outlet flow. The steady-state induction time for our measurable quantities is approximately 4 hours. Following this approach, our experiments can run for several days using a constant aerosol source. The typical throughput flow is 20 L min^-1, providing a calculated residence time of 3.9 h. The contents of the chamber are well mixed.

The injection system for precursor gases, which consists of solenoid valves and mass flow controllers, regulates flow rates within 1% accuracy and precision. Propene, NO, and NO₂ are drawn from cylinders containing 300 ppmv dilutions of each gas in N₂ (Spectra Gas). Clean air is generated by removing hydrocarbons, H₂O, and NO_x from compressed air (Aadco Model 737-14A pure air generator). Ozone is synthesized by passing pure air over a UV lamp (Jelight 600). Relative humidity is regulated by passing a variable flow of clean air through a bubbler containing 18 Mω cm water. Ozone, RH, NOx are computer-controlled to be at constant levels through a Labview interface. The volatile-organic-carbon molecules, which are obtained commercially (Aldrich), are introduced by injecting a known volume from a heated bulb flushed with clean air. As desired, seed particles can also be injected by an atomizer.