FOREWORD ASHRAE RP-1287 presented several recommendations related to particle counter specifications@ and SSPC 52.2 reviewed the findings and incorporated a number of those recommendations into this addendum. In addition@ input from several particle counter manufacturers was obtained to help ensure that the proposed recommendations are achievable and practical. These changes are to improve the reproducibility of the test. For that reason@ the particle counter is limited to one class of counters@ specifically light-scattering optical particle counters@ which are currently in wide use. Additionally@ stringent requirements on the particle counter's sizing resolution@ calibration@ sampling rate@ and other performance factors are specified. This addendum intends to make the specifications sufficiently (but not excessively) stringent and comprehensive in order to provide significantly improved reproducibility. Note: In this addendum@ changes to the current standard are indicated in the text by underlining (for additions) and (for deletions) unless the instructions specifically mention some other means of indicating the changes.