Long‐term atmospheric NOx/CO enhancement ratios in megacities provide evaluations of
emission inventories. A fuel‐based emission inventory approach that diverges from
conventional bottom‐up inventory methods explains 1970–2015 trends in NOx/CO
enhancement ratios in Los Angeles. Combining this comparison with similar measurements
in other US cities demonstrates that motor vehicle emissions controls were largely
responsible for US urban NOx/CO trends in the past half century. Differing NOx/CO …

Accurate knowledge of tropospheric ozone is important for understanding its effects on
human health, air quality, and climate. Global chemistry models generally have problems
reproducing tropospheric ozone concentrations, seasonal cycles and interannual trends.
Successful tropospheric ozone simulations require high quality information on the emissions
of ozone precursors, including nitrogen oxides (NOx), carbon monoxide (CO) and volatile
organic compounds (VOCs). Long-term measurements of NOx and CO have been made for …