Division 9.2.1 Diluent conditions and background concentrations

Gaseous constituents may be measured raw or dilute whereas PM measurement generally requires dilution. Dilution may be accomplished by a full flow or partial flow dilution system. When dilution is applied then the exhaust gas may be diluted with ambient air, synthetic air, or nitrogen. For gaseous emissions measurement the diluent shall be at least 288 K (15 °C). For PM sampling the temperature of the diluent is specified in points 9.2.2 for CVS and 9.2.3 for PFD with varying dilution ratio. The flow capacity of the dilution system shall be large enough to completely eliminate water condensation in the dilution and sampling systems. De-humidifying the dilution air before entering the dilution system is permitted, if the air humidity is high. The dilution tunnel walls may be heated or insulated as well as the bulk stream tubing downstream of the tunnel to prevent the precipitation of water-containing constituents from a gas phase to a liquid phase (‘aqueous condensation’).

Before a diluent is mixed with exhaust gas, it may be preconditioned by increasing or decreasing its temperature or humidity. Constituents may be removed from the diluent to reduce their background concentrations. The following provisions apply to removing constituents or accounting for background concentrations:

1. (a)

   Constituent concentrations in the diluent may be measured and compensated for background effects on test results. See Annex VII for calculations that compensate for background concentrations;

2. (b)

   The following changes to the requirements of sections 7.2, 9.3 and 9.4 are permitted for measuring background gaseous or particulate pollutants:

   1. (i)

      It shall not be required to use proportional sampling;

   2. (ii)

      Unheated sampling systems may be used;

   3. (iii)

      Continuous sampling may be used irrespective of the use of batch sampling for diluted emissions;

   4. (iv)

      Batch sampling may be used irrespective of the use of continuous sampling for diluted emissions.

3. (c)

   To account for background PM the following options are available:

   1. (i)

      F1For removing background PM, the diluent shall be filtered with high-efficiency particulate air (HEPA) filters that have an initial minimum collection efficiency specification of 99,97 % (see Article 1(19) for procedures related to HEPA-filtration efficiencies);

   2. (ii)

      For correcting for background PM without HEPA filtration, the background PM shall not contribute more than 50 % of the net PM collected on the sample filter;

   3. (iii)

      Background correction of net PM with HEPA filtration is permitted without pressure restriction.