Detail of GB/T 42660-2023

Introduction of GB/T 42660-2023

GB/T 42660-2023 Aerosol particle number concentration - Calibration of condensation particle counters 1 Scope This standard describes methods to determine the detection efficiency of condensation particle counters (CPCs) at particle number concentrations ranging between 1cm-3 and 105cm-3, together with the associated measurement uncertainty. In general, the detection efficiency will depend on the particle number concentration, the particle size, and the particle composition. The particle sizes covered by the methods described in this standard range from approximately 5 nm to 1000 nm. The methods can therefore be used both to determine a CPC calibration factor to be applied across the range of larger particle sizes where the detection efficiency is relatively constant (the plateau efficiency), and to characterize the drop in CPC detection efficiency at small particle sizes, near the lower detection limit. These parameters are described in more detail in Annex A. The methods are suitable for CPCs whose inlet flows are between approximately 0.1L/min and 5L/min. This standard describes a method for estimating the uncertainty of a CPC calibration performed according to this standard. 2 Normative references The following referenced documents are indispensable for the application of this document. For dated references, only the edition cited applies. For undated references, the latest edition of the referenced document (including any amendments) applies. ISO 15900 Determination of particle size distribution - Differential electrical mobility analysis for aerosol particles 3 Terms and definitions For the purpose of this document, the following terms and definitions apply. 3.1 aerosol relatively stable system of solid or liquid particles suspended in gas 3.2 bipolar charger particle charge conditioner to attain the equilibrium, known size-dependent charge distribution by exposing aerosol particles to both positive and negative ions within the device Note: Exposing aerosol particles to an electrically neutral cloud of positive and negative gas charges with sufficiently high charge concentration and for a sufficiently long period of time leads to an equilibrium with the net charge of the aerosol nearly zero (also known as charge neutralization). 3.3 calibration operation that, under specified conditions, in a first step, establishes a relation between the quantity values with measurement uncertainties provided by measurement standards and corresponding indications with associated measurement uncertainties and, in a second step, uses this information to establish a relation for obtaining a measurement result from an indication Note 1: A calibration may be expressed by a statement, calibration function, calibration diagram, calibration curve, or calibration table. In some cases, it may consist of an additive or multiplicative correction of the indication with associated measurement uncertainty. Note 2: Calibration should not be confused with adjustment of a measuring system, often mistakenly called “self-calibration”, nor with verification of calibration. Note 3: Often, the first step alone in the above definition is perceived as being calibration. [Source: ISO/IEC Guide 99] 3.4 calibration aerosol charge conditioned and size classified primary aerosol with particle number concentration adjusted for the calibration measurement, as delivered by the flow splitter 3.5 calibration particle material material of the particles of the calibration aerosol 3.6 charge concentration concentration of the net electrical charges per unit volume Note 1: Charge concentration is the measurand of the FCAE Note 2: FCAE measurement can be displayed as charge concentration, CQ (e.g. in fC/cm3), charge number concentration, , (e. g. in cm-3) or electrical current, IFCAE, (e.g. in fA). Using the elementary charge, e, and the volumetric FCAE inlet flow rate, qFCAE, these displayed values are related as follows: Example: A charge concentration of 1 fC/cm³ corresponds to a charge number concentration of 6241 cm-3. When the volumetric FCAE inlet flow rate is 1L/min, the resulting electrical current is 16.67 fA. 3.7 charge conditioning process that establishes a steady state charge distribution on the sampled aerosol 3.8 coefficient of variation; CV ratio of the standard deviation to the arithmetic mean value 3.9 coincidence presence of more than one particles inside the sensing zone simultaneously Note: Coincidence error is related to particle number concentration, flow velocity through the sensing zone and size of sensing zone. 3.10 condensation particle counter; CPC instrument that measures the particle number concentration of an aerosol Note 1: The sizes of particles detected are usually smaller than several hundred nanometres and larger than a few nanometres. Note 2: In some cases, a CPC maybe called a condensation nucleus counter (CNC). Note 3: The CPC used as the reference instrument is called the “reference CPC” throughout this standard. Note 4: The CPC under calibration is called the “test CPC” throughout this standard. [Source: ISO 15900:2009, modified] 3.11 detection efficiency η ratio of the concentration reported by an instrument to the actual concentration at the inlet of the instrument 3.12 differential electrical mobility classifier DEMC classifier that is able to select aerosol particles according to their electrical mobility and pass them to its exit Note: A DEMC classifies aerosol particles by balancing the electrical force on each particle with its aerodynamic drag force in an electrical field. Classified particles are in a narrow range of electrical mobility determined by the operating conditions and physical dimensions of the DEMC. Classified particles can have different sizes due to difference in the number of charges that they have [Source: ISO 15900:2009, modified] 3.13 differential mobility analyzing system DMAS system to measure the size distribution of submicrometre aerosol particles consisting of a pre-conditioner, particle charge conditioner, DEMC, flow meters, a particle detector, interconnecting plumbing, a computer, and software suitable for size-distribution calculation [Source: ISO 15900:2009, modified] 3.14 diffusion loss reduction of particle number concentration due to thermal (or Brownian) and turbulent diffusion transport (e.g. to the walls of a transport tube) 3.15 electrometer device that measures electrical current of about 1 femtoampere (fA) and higher [Source: ISO 15900:2009, modified] 3.16 equivalent particle diameter d equivalent diameter of the sphere with defined characteristics which behaves under defined conditions in exactly the same way as the particle being described Note: Particle diameter (or simply diameter) used throughout this standard always refers to the electrical mobility equivalent diameter, which defines the size of charged particles with the same electrical mobility or the same terminal migration velocity in still air under the influence of a constant electrical field. 3.17 faraday-cup aerosol electrometer; FCAE electrometer designed for the measurement of electrical charge concentration carried by an aerosol Note: An FCAE consists of an electrically conducting and electrically grounded cup as a guard to cover the sensing element that includes aerosol filtering media to capture charged aerosol particles, an electrical connection between the sensing element and an electrometer circuit, and a flow meter. [Source: ISO 15900:2009, modified] 3.18 flow rate quantity (volume or mass to be specified) of a fluid crossing the transverse plane of a flow path per unit time Note: For the exact flow rate indication of gases, information on the gaseous condition (temperature and pressure) or the reference to a standard volume indication is necessary. 3.19 geometric standard deviation GSD acronym used in this standard for geometric standard deviation 3.20 laminar flow gas flow with no temporally or spatially irregular activity or turbulent eddy flow 3.21 lower limit of the plateau efficiency dmin, ref lower size limit for which a reference CPC can be applied for the calibration of a test CPC Note: This size limit depends on the CPC itself, but also to some extent on experimental conditions and on the particle type.

Contents of GB/T 42660-2023