Table 1.

Comparison of selected properties of ANPs and MNPs (Oberdörster et al. 2005; Stone et al. 2009; Xia et al. 2009; Brouwer 2009; Kumar et al. 2008a, b, c, d; Kumar et al. 2009a, b)

Characteristics	ANPs	MNPs
Source	Combustion	Engineering (controlled synthesis)
Most popular class	Volatile organics, sulpur compounds and carbonaceous agglomerates	Silver, TiO2 and CNTs
Physicochemical properties	Volatile or semi-volatile, scattering and absorption	Non–volatile, conductive, super–hard, optical absorption, magnetism (properties of MNPs differ from those of their bulk material)
Organic chemical content	High	Low
Metal impurities	Low	Varies
Atmospheric release	Intentional or incidental (fugitive)	Unintentional or incidental (fugitive) (during production, handling, use and disposal of MNP products)
Atmospheric life time	Low	Unknown (expected to be relatively larger than ANPs but depending on type)
Preferred measurement metric for regulation	Number	Unknown (number, mass or surface area)
General shape of particle number/size distributions	Bi–modal (changing continuously due to the effect of transformation processes)	Unimodal or bimodal depending on material
Exposure route	Oral, dermal, inhalation	Oral, dermal, inhalation or ingestion
Adverse health effects	Fairly well known	Largely unknown
Surface area/volume	High	High
Uniformity in shape, size and functionality	Low	High
Instruments generally used for measuring ambient number distributions	SMPS, DMS500, DMS50, ELPI, CPC, CNC, APS, FMPS, UFP, LAS	SMPS, CPC

Note that these are generic properties of MNPs which can differ depending on the material

SMPS scanning mobility particle sizer, DMS differential mobility spectrometer, ELPI electrical low pressure impactor, CPC condensation particle counter, CNC condensation nucleus counter, APS aerodynamic particle sizer, FMPS fast mobility particle sizer, UFP ultrafine particle monitor, LAS laser aerosol spectrometer