Modeling Ground Ozone Concentration Changes after Variations in Precursor Emissions and Assessing Their Benefits in the Kanto Region of Japan

Ozone trends and their sensitivity in global megacities under the warming climate

Tropospheric ozone formation depends on the emissions of volatile organic compounds (VOC) and nitrogen oxides (NOx). In megacities, abundant VOC and NOx sources cause relentlessly high ozone episodes, affecting a large share of the global population. This study uses data from the Ozone Monitoring Instrument for formaldehyde (HCHO) and nitrogen dioxide (NO2) as proxy data for VOC and NOx emissions, respectively, with their ratio serving as an indicator of ozone sensitivity. Ground-level ozone (O3) reanalysis from the Copernicus Atmosphere Monitoring is used to assess the O3 trends. We evaluate changes from 2005 to 2019 and their relationship with the warming environment in 41 megacities worldwide, applying seasonal Mann-Kendall, trend decomposition methods, and Pearson correlation analysis. We reveal significant increases in global HCHO (0.1 to 0.31 × 1015 mol cm-2 year-1) and regionally varying NO2 (-0.22 to 0.07 × 1015 mol cm-2 year-1). O3 trends range from -0.31 to 0.70 ppb year-1, highlighting the relevance of precursor abundance on O3 levels. The strong correlation between precursor emissions and increasing temperature suggests that O3 will continue to rise as climate change persists.

Inorganic PM2.5 reduction in Kanto, Japan: The role of ammonia and its emission sources control strategies

Ammonia (NH3) is attracting attention as a carbon-free energy source and a significant precursor to inorganic PM2.5 (hereafter PM2.5), aside from NOx and SOx. Since the emission of NH3 has often been overlooked compared to NOx and SOx, this study aims to reveal the role of NH3 and its emission control on PM2.5 in Kanto, Japan. With the aid of gas ratio (GR) quantitatively defining the stoichiometry between the three precursors to PM2.5, and the aid of atmospheric modeling software ADMER-PRO, coupled with thermodynamics calculations, the spatiotemporal distribution along with PM2.5 reduction under different NH3 emission cutoff strategies in Kanto had been revealed for the first time. The cutoff of NH3 emission could effectively reduce the PM2.5 concentration, with sources originated from agriculture, human/pet activities, and vehicle sources, overall giving a 93.32% PM2.5 reduction. Different cutoff strategies lead to distinct reduction efficiencies of the overall and local PM2.5 concentrations, with GR as a crucial factor. The regions with GR ∼1, are sensitive to the NH3 concentration for forming PM2.5, at which the NH3 reduction strategies should be applied with high priority. On the other hand, installing a new NH3 emission source should be avoided in the region with GR < 1, suppressing the so-yielded PM2.5 pollution. The future PM2.5 pollution control related to the NH3 emission control strategies based on GR, which is stoichiometry-based and applicable to regions other than Kanto, has been discussed.