Our study is the second after Wang et al. (2013a) to place the
simulations in the future.Wang et al. performed global simulations,
with a higher resolution focus area over the US territory. Their
baseline emission scenarios are based on the IPCC-SRES growth
scenarios A1F1 and B1 (Nakicenovic et al., 2000), combined with
present-day fossil fuel burning emission factors. The simulations
using these baseline scenarios predict significantly increased air
pollution in 2050 compared to present, which is in contrast to our
baseline being the relatively clean CLE2020 scenario. Therefore, in
their simulation, the air quality then improves significantly,
compared to the highly polluted future baseline, when switching
all the road traffic to H2.