Analysis of the vertical temperature structure in the Bergen valley, Norway, and its connection to pollution episodes

Abstract

The vertical temperature profile in the lowest 1000 m of the atmosphere determines a number of important physical processes and meteorological phenomena such as high concentrations of anthropogenic air pollutants in urban areas. Long-term monitoring of temperature profiles at high vertical and temporal resolution has only become feasible only recently with the introduction of affordable angular scanning microwave temperature profile radiometers. In this study, we analyzed 2 years of continuous temperature profile measurements with the MTP-5HE instrument in the urbanized coastal Bergen valley, Norway. The data have a 10 min temporal and 50 m vertical spatial resolution, thus, constituting a unique data set for a microclimatic characterization of the atmosphere in this high-latitude valley. We studied a 2 year record of ground-based (G-) and elevated (E-) inversions, their dynamics and connection to large-scale circulations, and the links between the urban air quality and the temperature inversions. G-inversions are commonly observed during wintertime nocturnal hours. The local topographic features allow for the frequent occurrence of G-inversions, even during strong winds of up to 16 m/s. E-inversions exist mostly during spring and summer and only during unusual synoptic circulation with large-scale warm air advection directly above the valley. Events with high air pollution, identified based on measurements of NO 2 and particulate matter concentrations, are highly dependent on the existence of G-inversions. Meteorological models poorly capture both G-inversions and E-inversions reducing their utility for the assessment of urban air quality and local weather forecasts.

A proxy for air quality hazards under present and future climate conditions in Bergen, Norway

“…To fulfil the requirement on the circulation we utilized the wind at the 1000 hPa pressure surface as the relevant large-scale wind field according to the Jonassen et al (2012) and Wolf et al (2014) studies. The air quality hazards are furthermore associated with lower than climatological surface air temperatures (2 m level temperature).…”

“…2). Air quality hazards occur almost exclusively under low-level temperature inversions in connection with low cloudiness and weak winds during the extended winter season from November through February (Wolf et al, 2014). Under such conditions the damped vertical turbulent mixing in the valley allows the emitted pollutants to accumulate over several days.…”

“…The background colour shading shows the interpolated vertical profiles of the temperature lapse-rate per 100 m. The underlying temperature profiles were measured with a 50 m vertical resolution between 45 and 1045 m.a.s.l. in Bergen with the MTP-5HE microwave temperature profiler (Wolf et al, 2014). Data gaps (no colour shading) correspond to the presence of lowlevel clouds or precipitation .…”

Accuracy of retrieving temperature and humidity profiles by ground-based microwave radiometry in truly complex terrain

“…Comparison with radiosondes launched at a distance of 50 km provided accuracies of about 2 K in the lower troposphere. A MTP-5HE (by ATTEX) was used in the Bergen Valley (Wolf et al, 2014) in order to obtain temperature profiles and compare them with 1-year measurements from two automatic meteorological stations, located at the ground and on a mountain about 550 m above the valley floor; they obtained an RMSE of 0.2 and 0.8 K for the two stations, respectively. Overall, a thorough assessment of a passive temperature profiler in complex terrain using close-by radiosondes seems to be missing.…”

Self-organized classification of boundary layer meteorology and associated characteristics of air quality in Beijing

“…Since most air pollutants are emitted or chemically produced within this layer, its evolution plays an important role in the transport, dispersion and deposition of air pollutants Fan et al, 2008;Whiteman et al, 2014;Platis et al, 2016;Wolf et al, 2014;Wu et al, 2013). The ABL structure is determined by complex interactions between atmosphere static stability and those mechanical processes (such as wind shear from synoptic or terrain-induced flows) (Stull, 1988).…”