@article{10.1021/acsestair.6c00227,
    author = {Li, Zongrun and Qian, Yu and Hu, Yongtao and Vasilakos, Petros and Odman, M. Talat and Russell, Armistead G.},
    title = {Comparison of
Chemical Transport Model and Observation
Derived Ozone-NOx-VOC Isopleths
for the South Coast Air Basin of California},
    journal = {ACS ES&T Air},
    year = {2026},
    month = {09},
    abstract = {We developed, applied, evaluated, and compared chemical
transport
model-based and observation-based methods for constructing ozone isopleths
used to understand ozone-emission relationships, focusing on the South
Coast Air Basin of California (SoCAB). The High-order Decoupled Direct
Method (HDDM) embedded in the Community Multiscale Air Quality (CMAQ)
model was applied under different emission levels to map out the sensitivities
of ozone levels to anthropogenic emissions of nitrogen oxides (NOx) and volatile organic compounds (VOCs).
Ozone concentrations and sensitivities to emissions simulated by CMAQ-HDDM
were used to develop ozone isopleth diagrams for monitoring locations
across the SoCAB, and those isopleths were compared with observation-derived
isopleths. The CMAQ-HDDM- and observation-derived isopleths reproduced
the observed ozone concentrations (R2 =
0.70 and 0.96, respectively) and showed better agreement, especially
at inland locations, which typically experience higher ozone levels
than central or coastal sites. The responses of ozone to NOx and VOC emissions were compared over time, based
on historical VOC and NOx emission levels.
The sensitivities to NOx emissions showed
a stronger correlation (R2 = 0.75) between
the CMAQ-HDDM- and observation-derived methods than the sensitivities
to VOC emissions (R2 = 0.18). For most
regions in SoCAB, both the CMAQ-HDDM- and observation-derived isopleths
indicate that the ozone regime has transitioned from VOC-limited to
NOx-limited around the late 2000s. As
a result, for equal absolute emission changes, further reductions
in NOx emissions are more effective than
comparable VOC controls in achieving future ozone decreases, with
greater confidence for inland cities in the SoCAB.},
    issn = {2837-1402},
    doi = {10.1021/acsestair.6c00227},
    url = {https://doi.org/10.1021/acsestair.6c00227},
    eprint = {https://pubs.acs.org/aeacd5/article-pdf/doi/10.1021/acsestair.6c00227/68440755/acsestair.6c00227.pdf},
}