Single Instrument Solution for Air Quality and Greenhouse Gas Monitoring in Cities

Observation of air pollutants and greenhouse gases with high selectivity and sensitivity is of great importance for our understanding of their sources and sinks. For air pollution modelling and validation of emission inventories measurements at various spatial and temporal scales are required. Infrared laser absorption spectroscopy is often the method of choice, offering outstanding performance and reliability. Most frequently, however, this technology is used in a “one-species-one-instrument” solution because of the narrow spectral coverage of DFB-lasers. This can be overcome by combining several Quantum Cascade Lasers (QCLs), providing unique solutions in compact laser absorption spectrometers for environmental monitoring of multiple species in a single instrument.

We combined multiple DFB-QCLs into a single, compact laser absorption spectrometer to measure up to ten different compounds. We present simultaneous atmospheric measurements of the greenhouse gases CO₂, N₂O, H₂O and CH₄, and the pollutants CO, NO, NO₂, O₃, SO₂ and NH₃ with a single instrument. Furthermore, the instrument performance, first field results and comparison to standard air-quality and greenhouse gas monitoring instrumentation are discussed. The results demonstrate that spectrometers using QCLs can serve as an all-in-one solution for environmental monitoring stations replacing up to seven instruments at once. Furthermore, due to their reduced size and robustness, they can be used on mobile platforms, opening up new applications of air quality and greenhouse gas monitoring in cities.