SPEXone as an air quality monitoring system

Abstract

Aerosols, also known as particulate matter, are tiny particles or droplets suspended in the atmosphere which interact with solar radiation. These particles are partly responsible for cloud formation and are detected amongst others in (forest fire) smoke, dust, volcanic ash or sulfates. Aerosols have a large influence on the Earth’s climate as well as on air quality. Currently, SPEXone is one of the most promising instruments considering aerosol research due to the versatile nature of measurement methods based on multiple-angle polarization observations. Therefore, the SPEXone instrument will be implemented aboard the PACE satellite, designed primarily for aerosol observations for climate research of the Earth. The PACE satellite will be launched by NASA in 2025. The measurements of SPEXone provides highly relevant information on aerosol type for source apportionment. This raises the question whether SPEXone can serve as a stand-alone air quality monitoring system, thereby responding to the increasing awareness of the importance of monitoring air quality worldwide. Thus, this thesis focuses on the applicability of the SPEXone instrument regarding air quality monitoring by investigating plume polarization detection based on two relevant use cases. In this study, the plumes were simulated according to Gaussian plume behaviour in combination with a collection of observation scenarios. SPEXone measurements were simulated by using a radiative transfer model and instrument noise model to simulate the degree of linear polarization at the satellite sensor. This study found that for very optimistic emission rates, plume detection was possible for about 90 percent out of 144 measurements and between 79 and 67 percent out of 144 measurements at a wavelength of 670 nm. However, lowering the emission rate to realistic values showed that, apart from some very rare cases, no detection was possible. This leads to the conclusion that polarization signatures from the emitted aerosols in the simulated plumes are too weak in order to be detected above the polarization signature of the background. Nonetheless, due to the complexity of aerosol modelling, not all contributing factors were given the same level of detail, i.e. varying microphysical properties and the exact influence of the vertical height profile of the plume. Future research needs to focus on these aspects in order to yield a conclusive result of the applicability of the SPEXone instrument regarding air quality monitoring. Additionally, a different approach to characterize the background noise may increase the probability for plume detection.