Development of Remote Optical Instrumentation for the Enhanced Detection of Airborne Environmental Toxins

The severity of wildfires in the United States are increasing and in the amount of acreage burned due to climate change and a sustained drought in the western part of the country. As a greater number of wildfires burn in the west, the amount of smoke produced becomes a health concern to the public. Wildfires release airborne toxins and hazardous air pollutants that cause adverse health effects to the public in high concentrations but are of principle concern to health officials as they have differential impacts on infants and children. Some of the airborne toxins released are carbonyl compounds such as: formaldehyde, acetaldehyde, acetone, acrolein, and methacrolein. An air quality index (AQI) is the primary method of reporting air quality and the attributed health effects to the public. However, an AQI cannot quantify select pollutants or reliably quantify the airborne toxins in situ. The development of a mid-IR and nonlinear Raman detection instrumentation would allow for more dependable collection of wildfire smoke data and the quantification of select carbonyl compounds. Wildfire smoke was collected over the summer of 2021 around southwestern Idaho using EPA method TO-11A to determine the reliability of the method against optical detection methods. The initial development of a compact LED-based mid-IR instrument was constructed and limits of detection and quantitation were determined. Nonlinear Raman methods were explored using the optical output from photonic crystal fibers, for which output characterization and the sensitivity, selectivity, and limits of detection will be evaluated for the potential development of a compact all fiber spectrometer with real time in situ capabilities in Idaho

High Repetition Rate Mid-Infrared Differential Absorption Lidar for Atmospheric Pollution Detection

Developments in mid-infrared Differential Absorption Lidar (DIAL), for gas remote sensing, have received a significant amount of research in recent years. In this paper, a high repetition rate tunable mid-infrared DIAL, mounted on a mobile platform, has been built for long range remote detection of gas plumes. The lidar uses a solid-state tunable optical parametric oscillator laser, which can emit laser pulse with repetition rate of 500 Hz and between the band from 2.5 μm to 4 μm. A monitoring channel has been used to record the laser energy in real-time and correct signals. Convolution correction technology has also been incorporated to choose the laser wavelengths. Taking NO2 and SO2 as examples, lidar system calibration experiment and open field observation experiment have been carried out. The observation results show that the minimum detection sensitivity of NO2 and SO2 can reach 0.07 mg/m3, and 0.31 mg/m3, respectively. The effective temporal resolution can reach second level for the high repetition rate of the laser, which demonstrates that the system can be used for the real-time remote sensing of atmospheric pollution gas