Pollution characterization and source identification of nitrogen-containing species in fine particulates: A case...

To identify the nitrogen sources in atmospheric particulate matter, the stable isotope technique has been proven as an effective method. In this study, PM_2.5 samples at different pollution levels were collected from March 2018 to February 2019 in Hefei to analyze and compare the chemical composition. The results showed that the concentrations of PM_2.5, total nitrogen (TN) and nitrogenous species, as well as the total nitrogen isotopic composition (δ¹⁵N) increased with the aggravation of pollution. Ammonium nitrogen (NH₄⁺-N, 54%) was the dominant nitrogen-containing specie during the whole campaign, followed by nitrate nitrogen (NO₃^--N, 34%) and organic nitrogen (ON, 12%). The δ¹⁵N was positively correlated with NH₄⁺-N/TN but negatively correlated with NO₃^--N/TN. NH₄NO₃ and NH₄HSO₄ were the dominant forms of the secondary inorganic aerosols. In addition, a significant positive correlation was observed between the temperature and δ¹⁵N. Nitrogen source identification of PM_2.5 was conducted using Positive Matrix Factorization (PMF) model, δ¹⁵N values and Hybrid Single-Particle Lagrangian Integrated Trajectory (HYSPLIT) model. The results indicated that the contributions of the four main nitrogen sources were obtained and shown in descending order: combustion and industrial emission (42.06%) > secondary aerosols (24.04%) > vehicle exhaust (23.57%) > re-suspended dust (10.33%). The nitrogen aerosols might be mainly influenced by local emissions on normal and slight pollution days, while by both local emissions and transport from other areas on moderate and serious pollution days. Furthermore, nitrogen-containing species in PM_2.5 primarily originated from long/medium-distance transportation in two serious pollution events during the entire campaign.