Nitrate pollution deterioration in winter driven by surface ozone increase.

Recently, nitrate (NO₃^–) levels in winter pollution in eastern China have been increasing yearly and have become the main component of PM_2.5. The factors contributing to this rise in surface NO₃^– concentrations remain unclear, complicating the development of targeted pollution control measures. This study utilizes observational data from Shanghai during the winter 2019, alongside box model simulations, to recreate the NO₃⁻ pollution event and identify the key factors in the growth process. The analysis demonstrated that a rise in winter ozone levels significantly promotes NO₃^– production by facilitating NO_x conversion via gas-phase and heterogeneous reactions. These findings could explain the correlation between the synchronous increase of surface ozone and NO₃⁻ in recent years. Furthermore, simulation of control strategies for NO_x and volatile organic compounds (VOCs) identified an approach centered on ozone reduction as notably effective in mitigating winter NO₃^– pollution in the Yangtze River Delta. [ABSTRACT FROM AUTHOR]