Chemical characteristics of haze during summer and winter in Guangzhou

Airborne particles were collected with a 10-stage MOUDI and a PM₁₀ sampler in Guangzhou, China, during both haze and normal days in the summer of 2002 and 2003, and winter 2002. The characteristics of PAHs, organic carbon, elemental carbon and water-soluble inorganic ions were studied under four periods (summer normal, summer haze, winter normal and winter haze). In this study, secondary pollutants (OC, SO₄²⁻, NO₃⁻ and NH₄⁺) were the major chemical components and appeared to show a remarkably rapid increase from normal to haze days. The particle mass size distributions were bimodal and dominated by fine particles in haze days. A significantly higher OC/EC ratio was found in haze days (3.2–4.7) compared to normal days (1.8–2.8), indicating secondary organic aerosol formation might be significant during haze days. Correlation analysis between visibility and chemical species showed that the major scattering species were TC (total carbon) and sulfate in normal days and nitrate and TC in haze days, respectively. Simultaneously, correlation analysis between visibility and meteorological factors demonstrated that visibility increased with both temperature and wind speed, while it decreased with relative humidity. Furthermore, the relatively higher value of IcdP/(BghiP + IcdP) and the low value of Cmax, CPI, and BghiP/BeP in winter haze could be due to the growth of motor vehicle usage and energy consumption in winter.