Stability assessment from surface-based temperature measurements

Stability within the Planetary Boundary Layer is one of the key atmospheric parameters affecting turbulent diffusion of pollutants and consequently air quality. Static stability is normally assessed by measuring vertical profiles of temperature and humidity in the free atmosphere. This can be done using remote sensing techniques like radio acoustic sounding systems, or in-situ measurements such as radiosondes or tethersondes – all of which can be expensive. One cost-effective approach in mountain/valley terrain is to use surface-based temperature and humidity measurements over a range of topographic elevations to assess the free atmosphere vertical profiles within the valley. There are potential problems with this approach: surface-based measurements are strongly influenced by sensible and latent heat fluxes emanating from the surface, anabatic and katabatic flows may alter thermal fields, etc. In this study, 18 temperature and humidity loggers are installed from August 2003 until the present time along the side of a valley and up a nearby mountain between 566 m and 1235 m above sea level starting at 20 m vertical resolution in the valley of Prince George, British Columbia. The data from the surface-based profiles are compared with twice-daily high-resolution radiosonde observations that are linearly interpolated onto the surface station elevations. The ability of the surface-based measurements to replicate free-air profiles is assessed, and reasons for discrepancies investigated. In addition, the surface-based profiles are used to create an "inversion index" that is compared with ambient levels of SO2, NOx, TRS, PM10, and PM2.5 from a central monitoring location.