Pollution characterization and source identification of nitrogen-containing species in fine particulates: A case study in Hefei city, East China

Abstract

To identify the nitrogen sources in atmospheric particulate matter, the stable isotope technique has been proven as an effective method. In this study, PM2.5 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 PM2.5, 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 PM2.5 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 PM2.5 primarily originated from long/medium-distance transportation in two serious pollution events during the entire campaign.