Characteristics, emission sources and health risk assessment of trace elements in size-segregated aerosols during haze and non-haze periods at Ningbo, China.

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To characterize trace elements from inhalable particles and to estimate human health risks, airborne particles at an urban area of Ningbo city during haze and non-haze periods from November 2013 to May 2014 were collected by a nine-stage sampler. Seventeen trace elements (Na, Mg, Al, K, Ca, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, As, Cd and Pb) were measured by inductively coupled plasma mass spectrometry (ICP-MS). The concentrations of trace elements are in the ranges of 0.51ngm-3 (Co) ~ 1.53µgm-3 (K) for fine particles (Dp < 2.1μm), and 1.07ngm-3 (Co) ~ 4.96µgm-3 (K) for coarse particles (2.1μm < Dp < 9.0μm) during the haze days, which are 1.15 -4.30 and 1.23- 7.83-fold as those of non-haze days, respectively. These elements could be divided into crustal elements (Na, Mg, Al, Ca, Ti, Fe and Co), non-crustal elements (Cu, Zn, Cd and Pb) and mixed elements (K, V, Cr, Mn, Ni and As) according to their enrichment factor values (EFs) and size distribution characteristics. Five emission sources of trace elements were identified by positive matrix factorization (PMF) modeling. The main sources of trace elements in fine particles are traffic emission (21.7%), coal combustion (23.6%) and biomass burning (32.1%); however, soil dust (61.5%), traffic emission (21.9%) and industry emissions (11.8%) are the main contributors for coarse particles. With the help of the multiple-path particle dosimetry (MPPD) model, it was found that deposition fractions of seventeen measured elements in the pulmonary region were in the range of 12.4%-15.1% and 6.66% -12.3% for the fine and coarse particles, respectively. The human health risk assessment (HRA) was employed according to the deposition concentration in the pulmonary region. The non-carcinogenic risk (HI) was below the safety limit (1.00). Nonetheless, the excess lifetime carcinogenic risk (ELCR) for adults increased by 2.42-fold during the haze days (2.06 × 10-5) as compared to that of non-haze days (8.50 × 10-6) in fine particles. Cr (VI) and As together contributed 96.5% and 96.3% of the integrated cancer risks during the haze and non-haze periods, respectively. Moreover, the related ELCR values in coarse particles were 36.7% and 62.8% of those in the fine particles for the non-haze period and haze period, respectively.