Seasonal variability of nitrite and nitrate molar concentrations in fine and coarse particulate matter in coastal urban-industrial environments, and the effect of meteorological conditions on molar ratios

The present study investigates the seasonal variation, atmospheric transformation, and source attribution of nitrite (NO2-) and nitrate (NO3-) in fine (PM2.5) and coarse (PM2.5-10) particulate matter collected over a period of one year in a coastal urban-industrial area characterised by diverse emission sources. A comprehensive measurement programme was conducted to analyse the seasonal dynamics and correlations of nitrogen species. The measurement of molar concentrations (nmol/m³) and nitrate/nitrite molar ratios, as well as meteorological parameters (including temperature, relative humidity, solar radiation, and rainfall), were the scientific basis of this study. The findings indicate that nitrate and nitrite concentrations are notably elevated during the winter months, particularly in the fine fraction. These concentrations exhibit a strong correlation with combustion emissions associated with heating and cold weather conditions, characterised by low-radiation atmospheric conditions. The nitrate/nitrite molar ratios were elevated during the winter months, indicating enhanced oxidative transformation processes influenced by thermodynamic conditions and primary emissions. Pearson's correlation coefficient analysis confirmed a substantial negative relationship between temperature and nitrogen species. This finding emphasises enhanced secondary formation under cold conditions, as well as the significant impact of insolation. The findings of this study provide valuable insights into the complex interplay between anthropogenic emissions, atmospheric chemistry, and meteorological factors in coastal industrial environments. The study under scrutiny here demonstrates the pivotal function of fine-mode nitrate contamination during the heating season and its attendant health ramifications, thus engendering a comprehensive comprehension of paramount importance for the effective management of air quality in such regions.