Numerical Simulations Of The Influence Of Large-scale Wind Farms On Air Pollution Forecast In The Northern China Plain

As a clean and renewable energy,wind power has gained rapid development in the past several decades.China has the largest installed wind power capacity in the world.Although wind turbines do not yield direct emission of air pollutants and greenhouse gases,they may alter the surface characteristics within wind farms,causing potential disturbance to or impact on local atmospheric conditions.In the present study,using the Weather Research and Foresting model coupled with Chemistry?WRF-Chem?combining two wind farm parameterization schemes?the increased aerodynamic roughness length scheme and the wind turbine drag force scheme?,we assessed quantitatively the influences of large-scale wind farms in northern China on PM_2.5forecasting and elucidated the linkages between the changes in PM_2.5 disturbed by the wind farms induced changes in meteorological conditions,including the wind speed,turbulence,and air temperature.Multiple scenario simulations were conducted to examine the sensitivity and responses of PM_2.5 concentrations to the presence of large-scale wind farms.The major findings of this modeling investigation is summarized below:?1?The modeling results identify a wind speed deficit within and around the large-scale wind farms.This wind speed deficit is larger in winter?January?than that in summer?July?.The increasing vertical turbulent mixing induced by wind turbines results in the increase of temperature at the hub-height and surface within and downstream of the wind farms in January.We found that the increase in air temperature at the hub-height is slightly larger than that near the surface.In July,there is also the perturbation of air temperature at the hub-height and surface boundary layer near the wind farms.Considering the increasing turbulent kinetic energy?TKE?produced by the wind turbine blade rotation,we infer that the increase of temperature near the surface and hub-height is mainly caused by the turbulent inversion effect.?2?PM_2.5 concentrations tend to be accumulated in the downwind region or the region to the south of the wind farms in the winter month.Forced by winds and turbulent activities disturbed by wind turbines,PM_2.5 concentrations within and around the wind farms changed markedly on an hourly,daily,and monthly basis.During the wintertime when northwest wind prevails,PM_2.5 concentration decreases within the wind farm and in the upstream area,but increases in the downstream area of the wind farm.In summer,southeasterly summer monsoon prevails over the Northern China Plain.However,due to strong local atmospheric circulations,no dominant wind direction was identified.No significant changes in PM_2.5 concentrations were found in the wind farm but hourly PM_2.5 concentrations were perturbed in the vicinity of the wind farm and at a longer distance.We conclude that the changes in PM_2.5 concentrations caused by wind farms can be attributed to boundary layer dynamic and thermodynamic associated with wind turbine,which disturbs horizontal wind speed and turbulent energy,causing the horizontal and vertical mixing of PM_2.5.The changes in the air temperature at different heights within and around wind farms are conducive to PM_2.5 perturbation and diffusion.?3?Compared with the case without the presence of large-scale wind farms in the Northern China Plain,our results show that hourly PM_2.5 concentrations near and hundreds kilometers downstream of wind farms were fluctuated markedly with concentration fractions as high as 150%-400%.Such hourly concentration perturbation is particularly evident in winter,which may bring uncertainties to the air quality forecast.As a result,the influences of large-scale wind farms on PM_2.5 forecast should not be overlook.