Adtot	The total area of the downward-facing interior surface (m2)
Ai	Area of interior surface i (m2)
Cf(d)	Concentration associated with Mf(d) (µg·µg−1 Particulate matter)
Cin	Indoor concentration (µg·m−3)
Cout	Outdoor concentration (µg·m−3)
Cp (d)	Mass concentration sorbed to particulate matter (PM) in the air compartment (µg·µg−1 PM)
Cp0 (d)	Mass concentration sorbed to PM in the outdoor air (µg·µg−1 PM)
CpADJ0 (d)	Mass concentration sorbed to PM in the adjoining room (µg·µg−1 PM)
CPk(d)	Concentration associated with MPk(d)
Cterp	Concentration of a reactant (µg·m−3)
CV	Concentration in the vapor phase of the air compartment (µg·m−3)
CV0	Concentration in the vapor phase of the outdoor air (µg·m−3)
CVADJ0	Concentration in the vapor phase of the adjoining room (µg·m−3)
d	Aerodynamic diameter of PM (µm)
ds	First-order decay rate constant combining all sink processes (h−1)
e	Filter efficiency of the mechanical ventilation system (dimensionless)
e(d)	Filter efficiency of the mechanical ventilation system of PM (dimensionless)
ercl	Efficiency of the indoor filter device (dimensionless)
ercl (d)	Filter efficiency of the indoor recirculation device of PM (dimensionless)
Esi	Emission rate from the interior surface i (µg·h−1·m−2)
EVj	Emission rate from indoor source j other than interior surfaces (µg·h−1)
ffilt	Fractional runtime of the HVAC system if applicable (dimensionless, ranging from 0 to 1)
Jcoag	Coagulation term for gain or loss of the target size particle (µg·m−3·h−1)
JSVOC	SVOC loss as gas phase and gain as particle phase (µg·m−3·h−1)
k	Bimolecular reaction rate constant between two gas-phase compounds(m3·µg−1·h−1)
KV	First-order reaction rate constant in the gas phase (h−1)
M (d)	PMs mass concentration in the air compartment (µg PM·m−3)
M0 (d)	PMs mass concentration in the outdoor air (µg PM·m−3)
MADJ0 (d)	PMs mass concentration in the air of the adjoining room (µg PM·m−3)
Mf(d)	PMs concentration on the floor surface (µg PM·m−2)
MPk(d)	PMs emission rate from indoor source k (µg PM·h−1)
P	Penetration factor through cracks (dimensionless, often close to 1)
QADJ0	Volumetric flow rate from the adjoining room (m3·h−1)
Qcf	Volumetric flow rate of air through cracks (m3·h−1)
Qexhaust	Airflow rate of any mechanical exhaust ventilation system (m3·h−1)
Qfilt	Airflow rate through the central HVAC filter if applicable (m3·h−1)
Qmv	Volumetric flow rate of air drawn to the mechanical ventilation system (m3·h−1)
Qra	Volumetric flow rate of return air to the mechanical ventilation system (m3·h−1)
Qrcl	Air recirculation rate of the indoor filter device (m3·h−1)
Qwindow	Natural airflow through the window opening (m3·h−1)
Rsus	Resuspension rate coefficient from surface to indoor air (h−1)
S	Indoor source strength (mass emission rate) (µg·h−1)
t	Time (h)
V	Volume of the compartment (m3)
vdep	Deposition velocity from indoor air to surface (m·h−1)
β	The first-order indoor loss rate by deposition to surfaces and/or surface reactions (h−1)
ηfilt	Removal efficiency of a filter installed in the HVAC system if applicable (dimensionless, ranging from 0 to 1)
ξ	Secondary organic aerosols yield
Ψgas	The production or removal rate of a species due to gas-phase reaction (µg·m−3·h−1)
λ	Air exchange rate (h−1)
λd	Deposition rate of particles or gas species on indoor surfaces (h−1)
λinf	Air exchange rate due to infiltration alone (h−1)
λnat	Air exchange rate due to the natural ventilation (h−1)