With urbanization, anthropogenic water vapor emissions have become a
significant component of the urban atmosphere. Fossil fuel
combustion-derived vapor (CDV) is a primary source of these emissions.
Owing to the notably low CDV d-excess, stable hydrogen and oxygen
isotopes are promising for distinguishing CDV from natural sources.
Considering the limitations of in situ observations, this study aims to
explore the feasibility of using IsoRSM, an isotopically enabled
regional atmospheric model, to simulate CDV emissions in urban areas in
winter. Two experiments were conducted: one in Salt Lake City in January
2017 and another in Beijing in January 2007. The simulation results
showed that the CDV addition significantly reduced the water vapor
d-excess, particularly when the boundary layer was stable. The
simulation with CDV emissions aligned better with the time series of in
situ observations in Salt Lake City. The modification led to a more
pronounced positive correlation between vapor d-excess and specific
humidity, which was similar to the observation of Salt Lake City. The
CDV inclusion significantly increased the vapor d-excess variability
with varying wind directions in both sites. However, in Beijing, the
underestimation of d-excess variation from natural sources caused a
bigger discrepancy between the observed and simulated d-excess and CDV
fraction. Thus, though there were still biases, the inclusion of CDV
could improve the accuracy of isotopic simulation in the urban regions
where CDV was one of the controlling factors of vapor d-excess.