Effects of low-carbon energy adoption on airborne particulate matter concentrations with feedbacks to future climate over California

<p>California plans to reduce emissions of long-lived greenhouse gases (GHGs) through adoption of new energy systems that will also lower concentrations of short-lived absorbing soot contained in airborne particulate matter (PM). Here we examine the direct and indirect effects of reduced PM concentrations under a low-carbon energy (GHG-Step) scenario on radiative forcing in California.&nbsp; Simulations were carried out using the source-oriented WRF/Chem (SOWC) model over California with 12 km spatial resolution for the year 2054. The avoided aerosol emissions due to technology advances in the GHG-step scenario reduce ground level PM concentrations by ~8.85% over land compared to the Business as Usual (BAU) scenario, but changes to meteorological parameters are more modest.&nbsp; Top of atmospheric forcing predicted by the SOWC model increased by 0.15 W m^-2, surface temperature warmed by 0.001 K, and planetary boundary layer height (PBLH) increased by 2.20 cm in the GHG-Step scenario compared to the BAU scenario. PM climate feedbacks are small because the significant changes in ground level PM concentrations associated with the GHG-Step scenario are limited to the first few hundred meters of the atmosphere, with little change for the majority of the vertical column above that level.&nbsp; As an order-of-magnitude comparison, the long-term effects of global reductions in GHG emissions (RCP8.5 &ndash; RCP4.5) lowered average surface temperature over the California study domain by approximately 0.76 K. &nbsp;The effects of long-lived climate pollutants such as CO₂ are much stronger than the effects of short-lived climate pollutants such as PM soot over California in the year 2054.&nbsp;</p>