Uncertainties in mitigating aviation non-CO₂ emissions for climate and air quality using hydrocarbon fuels

Abstract

The effects of aviation's non-CO2 emissions on climate and air quality are complex and relatively poorly understood. Mitigation measures need to be very carefully considered so that perverse outcomes do not result.

The Social Costs of Aviation: Comparing Contrail Cirrus and CO2

“…This temporal difference in climate impacts is critical when evaluating mitigation options and policy instruments for the aviation sector. For instance, rerouting flights may be one way to reduce the formation of contrails, but that may increase CO₂ emissions (Lee et al, 2023;Geraedts et al, 2024;Borella et al, 2024). To make informed decisions regarding re-routing of flights, fuel choices, engine development and other potential measures, the climate impacts of different forcers must be made comparable.…”

“…Consequently, contrails have a much smaller warming impact daytime and may even have a net cooling effect (Meerkötter et al, 1999). Further, ice-supersaturated regions tend to be highly variable in both space and time and hard to forecast (Lee et al, 2023). Hence, the properties of contrail cirrus depend highly on both ambient and aircraft conditions, causing large spatio-temporal variabilities in the formation of contrail cirrus and its warming properties.…”

Characterizing and Predicting nvPM Size Distributions for Aviation Emission Inventories and Environmental Impact

“…Central to these concerns is the issue of nonvolatile particulate matter (nvPM) emissions from aircraft engines, which impact atmospheric chemistry, radiative forcing, and human health. − A key aspect of understanding nvPM’s environmental impact is its particle size distribution (PSD). The PSD is critical because it determines the particles’ residence time in the atmosphere, their health effects, their interaction with solar radiation, and their potential to form contrail and cloud condensation nuclei, one of the most uncertain aspects of aviation’s climate impacts. , …”

“…The PSD is critical because it determines the particles' residence time in the atmosphere, their health effects, their interaction with solar radiation, and their potential to form contrail and cloud condensation nuclei, one of the most uncertain aspects of aviation's climate impacts. 4,5 Historically, PSD measurements in aircraft engine exhaust were used to estimate nvPM emission indices (EI, amount of pollutant per kg fuel burned) at ground level and cruising altitudes. 6−8 Electrical mobility-based sizing instruments have reported high number concentrations of ultrafine particles in exhaust plumes, challenging the adequacy of the traditional smoke number (SN) standard, which focused primarily on visibility impacts.…”

“…The PSD is critical because it determines the particles’ residence time in the atmosphere, their health effects, their interaction with solar radiation, and their potential to form contrail and cloud condensation nuclei, one of the most uncertain aspects of aviation’s climate impacts. 4 , 5 …”