AEROSOL_NOTES - 28 September 2006


1.  N2O5 Hydrolysis.  Updated heterogeneous reaction probability:

    Since CMAQ v4.3, the heterogeneous reaction probability for N2O5
    hydrolysis was computed as a function of aerosol nitrate and sulfate
    concentrations. Recent laboratory evidence indicates that the
    probability is also influenced by temperature and relative humidity.
    Thus, the reaction probability has been changed so it is now a function
    of sulfate, nitrate, temperature, and relative humidity.  To assist
    model users, the N2O5 heterogeneous reaction probability (i.e.,
    GAMMA_N2O5) has been added as a new variable to the AERODIAM diagnostic
    output file.

2.  ISORROPIA.  Incorporated Version 1.7 of ISORROPIA:

    ISORROPIA is an aerosol equilibrium model used by the CMAQ aerosol
    model.  An updated version of ISORROPIA, released by Dr. Athanasios
    Nenes of Georgia Tech in March 2006, has been incorporated into CMAQ.
    The most significant change from the version of ISORROPIA in CMAQ 4.5.1
    is the correction of a bug in how activity coefficients are adjusted
    for temperatures other than 298 K.  Tabulated activity coefficients
    were previously not adjusted at 273 K when they should have been.  This
    affects temperatures in the range 260.5 - 285.5 K.

3.  Aerosol Water.  Upper limit of input RH for ISORROPIA:

    Very high concentrations (e.g., 1000 ug/m3) of aerosol water were
    obtained in previous versions of CMAQ.  Aerosol water is a direct
    output of ISORROPIA.  In consultation with Uma Shankar, Dr. Athanasios
    Nenes, and Dr. Francis Binkwoski, we have set an upper limit of 95% RH
    on the input to ISORROPIA so that the output concentrations of aerosol
    H2O would not resemble cloud- or fog-like conditions.  This problem was
    reported by Dr. Yang Zhang of NC State, and alluded to previously by
    Dr. Weimin Jiang of NRC-Canada and Dr. Jinyou Liang of CARB.