Influence of future anthropogenic emissions on climate, natural emissions, and air quality

This study examines the effects of future anthropogenic emissions on climate, and the resulting feedback to natural emissions and air quality. Speciated sector- and region-specific 2030 emission factors were developed to produce gas and particle emission inventories that followed Special Report on Emission Scenarios (SRES) A1B and B1 emission trajectories. Current and future climate model simulations were run, in which anthropogenic emission changes affected climate, which fed back to natural emissions from lightning (NO, NO2, HONO, HNO3, N2O, H2O2, HO2, CO), soils (dust, bacteria, NO, N2O, H2, CH4, H2S, DMS, OCS, CS2), the ocean (bacteria, sea spray, DMS, N2O, H2, CH4), vegetation (pollen, spores, isoprene, monoterpenes, methanol, other VOCs), and photosynthesis/respiration. New methods were derived to calculate lightning flash rates as a function of size-resolved collisions and other physical principles and pollen, spore, and bacteria emissions. Although the B1 scenario was ‘‘cleaner’’ than the A1B scenario, global warming increased more in the B1 scenario because much A1B warming was masked by additional reflective aerosol particles. Thus neither scenario is entirely beneficial from a climate and health perspective, and the best control measure is to reduce warming gases and warming/cooling particles together. Lightning emissions declined by ~3% in the B1 scenario and ~12% in the A1B scenario as the number of ice crystals, thus charge-separating bounceoffs, decreased. Net primary production increased by ~2% in both scenarios. Emissions of isoprene and monoterpenes increased by ~1% in the A1B scenario and 4–5% in the B1 scenario. Near-surface ozone increased by ~14% in the A1B scenario and ~4% in the B1 scenario, reducing ambient isoprene in the latter case. Gases from soils increased in both scenarios due to higher temperatures. Near-surface PM2.5 mass increased by ~2% in the A1B scenario and decreased by ~2% in the B1 scenario. The resulting 1.4% higher aerosol optical depths (AODs) in the A1B scenario decreased ocean wind speeds and thus ocean sea spray and bacteria emissions; ~5% lower AODs in the B1 scenario had the opposite effect.