Aircraft Measurement of Chemical Characteristics of PM 2.5 over the Yangtze River Area in China

To study the vertical distributions of PM2.5 mass and chemical components over the Yangtze River area, PM2.5 was sampled with filters over Changzhou, which is located in the eastern part of China, Shashi, which is located in the central part of China, and Xinjin, which is located in the western part of China, on the Yun-12 aircraft from August 21 to September 13, 2003. The samples were weighed for mass concentrations, and the chemical profiles of 8 inorganic ions (Cl−, NO3−, SO42−, Na+, NH4+, K+, Mg2+ and Ca2+), carbon fractions (organic carbon and elemental carbon) and 18 elements were analyzed in a laboratory. The mass concentrations at 400–1500 m were greater than those at 1600–3200 m, indicating the effect of ground surface sources. Similar PM2.5 compositions were found both at 400–1500 and 1600–3200 m. SO42− was the dominant ionic component, followed by NO3−, NH4+, Ca2+, K+, Na+, Cl− and Mg2+. Secondary inorganic ions (SO42−, NO3− and NH4+) contributed to 80–83% of the total ionic species, indicating that the role of secondary formation plays an important role in water-soluble ions. SO42− mainly existed as (NH4)2SO4. NH4+ was unable to completely neutralize SO42− and NO3−, and the deficit was approximately 32%. More than 70% of the Ca2+ contribution was derived from anthropogenic sources, which was related to construction activities and cement manufacturing. K+ was predominantly derived from anthropogenic sources (72.2–74.0%) and crustal sources (approximately, 23.3–24.9%). The OC/EC ratios at 1600–2800 m were greater than those at 500–1200 m, which was probably due to the presence of secondary products that were produced by photochemical smog activities during the uplifting of air masses.