Abstract

Evaluation of downscaled meteorological information is crucial to identifying model behaviors that may propagate to end-applications such as the simulation of local air quality. This study conducted and assessed year-long simulations of hourly meteorology over the Terrace–Kitimat Valley of northwestern British Columbia at 1-km horizontal gridding for six PBL schemes in the WRF version 4.0 model. In terms of key surface meteorological variables that affect air quality, simulations over land demonstrated better skill for specific humidity and wind direction, than for air temperature and wind speed. Spatial differences in modeled atmospheric properties and vertical profiles, especially for moisture content, were used to diagnose the relative capacity of each PBL scheme to represent pollution dispersion and dilution. Stable conditions at night increased suppression of boundary-layer mixing by the nonlocal YSU scheme compared with suppression by the local eddy-diffusion component of the ACM2 scheme, resulting in decreased wind speed and ambient temperature, but moister air with the YSU scheme. The weakening of mixing by the MYNN3 scheme with inland distance suggested that higher-order, nonlocal transport is sensitive to increasing topographic steepness towards the northern part of the valley. Disparities in mixing strengths amongst PBL schemes were greater in the summer when conditions were generally less stable with moist, warm air blowing inland than in winter when the valley channels cold, stable air from the interior. Increased convection in daytime led to greater entrainment of air from aloft and a thicker PBL with the YSU scheme than the ACM2 scheme in summer while increasing counter-gradient transport in the MYNN3 scheme that reduces dilution.

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