Size, composition, and mixing state of individual aerosol particlesin a South China coastal city

Aerosol samples were collected in summer in Macao, a coastal city of the Pearl River Delta Region in China. Morphology, size,elemental composition, and mixing state of individual aerosol particles were determined by scanning electron microscopy coupledenergy dispersive X-ray (SEM/EDX) and transmission electron microscopy (TEM). Based on the morphologies of 5711 aerosolparticles, they consist of soot (32%), mineral (17%), secondary (22%), and unknown fine particles (29%). The sizes of these particleswere mostly distributed between 0.1 and 0.4 m. Compositions of 202 mineral particles were obtained by SEM/EDX. Mineral particleswere mainly classified into three types: Si-rich, Ca-rich, and Na-rich. The compositions of typical mineral particles can indicate theirsources in sampling location. For example, mineral particles, collected along the main street, were associated with trace amounts ofheavy metals, such as Zn, Ti, Mn, Ba, Pb, and As. TEM observations indicate that most Na-rich particles were aged sea salt particles(e.g., Na2SO4 and NaNO3) which formed through heterogeneous chemical reactions between sea salt and acidic gases. Additionally,aging time of soot was short in Macao due to high humidity, high temperature, and high levels of sunlight in Macao. Most of soot andfine mineral dust particles were internally mixed with secondary particles.