Influence of Explicit Tropospheric VOC Chemistry on the Top‐Of‐Atmosphere Net Radiation Budget: Differences Between Two Preindustrial CESM2 Chemistry Configurations

Abstract The representation of volatile organic compound (VOC) chemistry in earth system models directly impacts aerosol formation. Previous work shows explicitly representing VOC chemistry produces significant impacts on simulated climate compared to an implicit “SOAG scheme” that prescribes a bulk gas‐phase precursor to secondary organic aerosol (SOA) formation. Here, we examine the top‐of‐atmosphere net radiation difference () between two chemistry configurations in the Community Earth System Model version 2 under preindustrial conditions using fixed sea surface temperature (fSST) simulations. We performed 150‐year fSST simulations in two configurations: (a) WF, with explicit VOC chemistry in the troposphere, and (b) MF, with a SOAG scheme in the troposphere. The computed due to explicit VOC chemistry is . Additional analysis indicates that the shortwave component of is associated with changes in aerosol optical depth and clear‐sky shortwave radiation, largely driven by widespread reductions in SOA optical depth. Longwave differences contribute to (roughly 45%) and are discussed separately, but the attribution analysis focuses on the shortwave component. Earlier studies have also found widespread SOA changes in response to explicit VOC chemistry, with associated impacts on aerosol optical depth, but the mechanisms remain unclear. 250‐year simulations using fully coupled versions of WF and MF (called “WC” and “MC”) are also performed. WC produces a higher baseline of global mean surface temperature (GMST), as expected given the positive . This result contrasts with an earlier study which produced nearly unchanged GMST. We discuss this contrast and our greater confidence in these results.