*2.3. Processing of Size-Fractionated Aerosol Concentration Data*

The utilization of portable aerosol instruments with different particle diameter ranges and cutoff diameters enables derivations of size-fractionated particle number and mass concentrations [47]: Super-micron (1–10 μm) particle number and mass concentrations, submicron (0.01–1 μm) particle number concentrations, PM2.5 mass concentrations, PM10 mass concentrations, and PM10–1 mass concentrations. Additionally, we derived the particle number size distribution *n*0 *<sup>N</sup>* <sup>=</sup> *dN dlog*(*Dp*) within eight diameter bins:


The particle mass size distribution was estimated from the particle number size distribution by assuming spherical particles:

$$m\_M^0 = \frac{dM}{d\log\left(D\_p\right)} = \frac{dN}{d\log\left(D\_p\right)}\frac{\pi}{6}D\_p^3\rho\_p = n\_N^0\frac{\pi}{6}D\_p^3\rho\_p\tag{1}$$

where *n*<sup>0</sup> *<sup>M</sup>* is the particle mass size distribution, *dM* is the particle mass concentration within a certain diameter bin normalized to the width of the diameter range *dlog Dp* of that diameter bin, *dN* is the particle number concentration within that diameter bin (also normalized with respect to *dlog Dp* to obtain the particle number size distribution, *n*<sup>0</sup> *<sup>N</sup>*), *Dp* is the particle diameter, and ρ*<sup>p</sup>* is the particle density, here assumed to be unit density (1 g cm−3). In practice, the particle density is size-dependent and variable for different aerosol populations (i.e., diesel soot vs. organic aerosol); therefore, size-resolved effective density functions should be used. However, there is limited empirical data on the effective densities of aerosols produced by indoor emission sources. Thus, the assumption of 1 g cm−<sup>3</sup> for the particle density will result in uncertainties (over- or underestimates, depending on the source) in the estimated mass concentrations.

The size-fractionated particle number concentration was calculated as:

$$PN\_{D\_{p2} - D\_{p1}} = \bigcap\_{D\_{p1}}^{D\_{p2}} n\_N^0(D\_P) \cdot d\log(D\_P) \tag{2}$$

where *PNDp*2−*Dp*<sup>1</sup> is the calculated size-fractionated particle number concentration within the particle diameter range *Dp*1*–Dp*2. Similarly, the size-fractionated particle mass concentration *PMDp*2−*Dp*<sup>1</sup> was calculated as:

$$P M\_{D\_{p2} - D\_{p1}} = \int\_{D\_{p1}}^{D\_{p2}} n\_M^0(D\_P) \cdot d\log(Dp) = \int\_{D\_{p1}}^{D\_{p2}} n\_N^0(D\_P) \frac{\pi}{6} D\_p^3 \rho\_{p'} d\log(Dp) \tag{3}$$

PM2.5 and PM10 can be also calculated by using Equation (3) and integrating over the particle diameter range starting from 10 nm (i.e., the lower cutoff diameter according to our instrument setup) and up to 2.5 μm (for PM2.5) or 10 μm (for PM10).
