Objectives To explore the concentration levels of heavy metals and metalloids on atmospheric particulate matter in a district of Nanjing, and to evaluate the characteristics and risks of the loading elements on the particles in the graded particle size.

Methods A PSW-8 aerosol particle size distribution sampler was used to collect atmospheric particulate matter samples in a district of Nanjing from November 23 to December 17, 2015. The concentration of atmospheric particulate matter with different particle sizes was determined by gravimetric method. The concentration of heavy metals and metalloid elements in different particle size particles were determined by microwave digestion-ICP/MS method. Environment health risks of heavy metals and metalloids of different particle sizes were assessed by environmental health risk assessment model recommended by the United States Environmental Protection Agency (US EPA).

Results The mass concentration and mass of (0.65~1.10) μm particle size in a district of Nanjing atmospheric particulate matter were the highest. The trend of heavy metal and metalloid concentration in (0.43~10) μm particulate matter was Al > Pb > Mn > Cu > Cr > Sr > As > Ni > Se > V > Rb > Cd > Bi > U > Co > Cs > Ag. 13 kinds of heavy metals and metalloid elements, namely Se, Pb, Ag, As, Bi, Cd, Cs, Rb, Ni, Cu, Cr, Mn and V, were mainly concentrated on particles with the size below 2.1 μm. U, Co, Sr and Al elements were mainly distributed in particles larger than 2.1 μm. The enrichment factors of U, Cr, Ni, Cu, Pb, As, Ag, Bi and Cd elements in each particle size segment were all greater than 10. As the particle size decreases, the enrichment factor of heavy metals became higher. The non-carcinogenic risks levels of elements were all lower than 1, and the carcinogenic risks levels of fine particle size section and whole particle size section were higher than 1.00×10^-6.

Conclusions The atmospheric particulate matter was mainly composed of particles below 2.1 μm during the sampling period. The heavy metals and metalloid elements with a great impact on the health of the population had a higher content in the fine particle size section. The enrichment factors and health risks of elements in the fine particle size section were higher. Research on small particle size particles and their loaded contaminants in atmospheric particulates should be strengthened.