Quantifying natural emissions and their impacts on air quality in a 2050s Australia

Abstract

Biogenic hydrocarbons, sea salt and dust emissions are driven by meteorological variables, which will change in a future climate. Natural emissions can dominate air quality in Australia, particularly when high biogenic activity promotes smog formation in summer. Therefore, quantifying how natural emissions might change is important. This study uses 4 downscaled Global Climate Models (GCMs) under 2 shared socioeconomic pathways in the 2050s to drive natural emissions at 20 km spatial resolution in the CSIRO Chemical Transport Model. Changes in air quality parameters were calculated by comparing each 5-year future run to a 5-year run from the current period. Higher urban air mass stagnancy was predicted in winter. When combined with lower rainfall increased particle residence time is expected. By contrast, higher ventilation indices were predicted in summer. Higher wind speeds in the ocean facilitated additional sea salt emissions. As Australian cities are largely coastal, sea salt contributed ∼35% of the1-2 μg m⁻³ extra coarse particulate matter predicted. Peak summertime isoprene emissions are set to double in 2050, by 3–4 mg m⁻² h⁻¹ in eastern Australia. This produced 3–6 ppb additional ozone in Australian cities already at air quality limits. Monoterpene emissions increased in 2050, but cooler night-time minimum temperatures led to decreased emissions in some GCMs. A reduced summertime oxidant capacity in Australian cities is likely driven by higher biogenic emissions. The lifetime of methane will increase by half a year in response, causing a warming feedback warranting further study using models with free running oxidant schemes.