Definition

Collocation is the process of checking the performance of an air sensor by installing and operating a sensor in proximity to a reference instrument(s). The process by which a sensor and a reference instrument are operated at the same time and place under real-world conditions. The siting criteria (e.g., proximity and height of the sensor and the reference monitor) should follow procedures outlined in 40 CFR Part 58 as closely as possible. For example, sensors should be placed within 20 meters horizontally of the reference instrument, positioned such that the sample air inlets for the sensors are within a height of ± 1 meter vertically of the sample air inlets of the reference instrument, and placed as far as possible from any obstructions (e.g., trees, walls) to minimize spatial and wind turbulence effects on sample collection.