def MER2unit(MER, M63=0.1):
    """Solving for unit mass - comparable to HYSPLIT output
    Inputs: MER in kg/s, mass fraction of fine ash (M63) Fine ash is < 63um according to Mastin et al. 2009. 
    The mass fraction of fine ash is highly variable and poorly known.
    Output: unit mass in grams (unit_mass), unit mass of fine ash in grams (mass63). 
    Assume model output is one unit mass (per hour - based on MER conversion)."""
    unit_mass = MER * 3600 * 1000
    mass63 = unit_mass * M63
    return unit_mass, mass63