2.1 User input
The tool requires user input on the following aspects:
In the product section of the input the parameters of the spray that determine exposure are specified. There are two aspects of the product that have a large impact on the potential exposure:
- The amount of nanomaterial that is released into air during use
- The size of the aerosol that acts as a carrier of the nanomaterial
The amount released from a spray is determined by its mass
generation rate and the time duration of the use of the spray (i.e.
how long the product is sprayed.) The emitted product will be a
mixture of various compounds such as propellants, solvents and the
nanomaterial itself. Only the nonvolatile components of the product
will end up as airborne aerosol particles as the volatile
components will vaporize and be released as a gas. In ConsExpo
nano, it is assumed that the nanomaterial is the dominant
non-volatile component and the contribution of other compounds to
the aerosol particle is neglected. Finally, if a spray is used on a
surface only a fraction will become airborne as most of the product
is expected to land on the surface.
The size of the aerosol is important for two reasons. First it determines how long the aerosol will be airborne. A smaller aerosol will be airborne for a longer stretch of time and thus have a higher potential for inhalation. Second, once inhaled, the aerosol size will determine its deposition in the respiratory tract and therefore its potential to reach the alveoli.
To specify the product the following input is required:
- Mass generation rate The amount of product released per unit time. The product will generally contain different components (e.g. propellant gas, solvents, the (non-volatile) nanomaterial itself.) The mass generation refers to the mass of this complete mixture. It is the value that would be measured when measuring the spray before use and after use divided by the time it was operated.
- Aerosol The aerosol is assumed to consist of spherical particles, the geometry of which is uniquely determined by its (aerodynamic) diameter.
- The type of distribution The diameter of the sprayed aerosol may be represented by a single number or as a (mass-based) lognormal distribution. In the case of a ‘monodisperse’ distribution, the aerosol diameter is specified by the value of the parameter ‘Aerosol diameter (median)’. In case of a ‘log normal’ distribution, the distribution is specified by the ‘Aerosol diameter (median)’, the ‘arithmetic coefficient of variation’ (defined as the arithmetic standard deviation divided by the mean). The distribution is taken to range from 0 to the ‘Maximum aerosol diameter’, above which the distribution is truncated.
In addition, the aerosol particle has a mass density, specified using the parameter:
- Density aerosol particle The mass density of the airborne aerosol particle generated by the product. It depends on the mass density of the nanomaterial itself and the stacking of nanoparticles (or their aggregates) in the aerosol particle. Could be set to the density of the nanomaterial if unknown.
- Weight fraction nanomaterial The fraction of the nanomaterial mass of the total product mass (as it is contained in the spray can).
- Airborne fraction The fraction that accounts for the fact that in using a spray on a surface, only part of the spray will end up as airborne aerosol, as the bulk of the material will end up on the treated surface. For an air space application (e.g. spray against flying insects, air freshener) the fraction will be close to 1. For a surface spray (e.g. a plant spray, all purpose cleaner), this fraction will be much lower. See