Table 5.

Linear regression equation results examining the relationship of aspiration fraction (A) and particle aerodynamic diameter (d_ae, μm)

ID	Linear regression equation	Coefficient of Determination (R2)	Comments
1	A = −5.0741 + 8.092log(dae) − 2.7016[log(dae)]2	0.8280	Form similar to Hsu and Swift (1999). Does not fit A ≅ 1 when dae is small.
2	A= 1.902 log(dae) − 0.8695 [log(dae)]2	0.9363	Form similar to Hsu and Swift (1999) without intercept. Does not fit A ≅ 1 when dae is small.
3	A= 1.168 − 0.00847dae	0.7851	Form of Aitken et al. (1999) with a fitted intercept. Decrease in A with increasing particle size. Overestimates A with small dae (A = 1.16 for dae = 1 μm).
4	A = 1.0365 − 0.0085dae + 0.02055Um	0.8806	Form similar to Aitken et al. (1999). Aspiration decreases with increasing particle size and increases with increasing mouth velocity. Shortcoming: A at dae =1 μm by as much as 28% over range of tests for high breathing velocity.
5	A = 1.2728 − 0.0085dae − 1.168(Uo/Um)	0.8603	Linear form, like ID-4, but using velocity ratio in place of Um. Coefficient of variation was reduced.
6	A= 0.8209 − 6.275 × 10−5dae2 + 0.0205Um	0.9186	Linear form using particle diameter squared. Aspiration behaves well, increasing with increased suction velocity and decreasing with increased particles size. For range tested, Um contributed 3.7–25% to aspiration estimates. A = 86% for dae = 1 μm at low and 107% for high suction.
7	A = 1.0582 − 6.251 ×10−5dae2 −1.168(Uo/Um)	0.8984	Linear form with dae2, like ID-6, but using velocity ratio in place of Um. Again, the coefficient of variation was reduced.

Other dependent variables identified as significant included mouth velocity (U_m = 1.81, 4.33, and 12.11 m s⁻¹) and freestream velocity (U_o = 0.2 and 0.4 m s⁻¹). Neither lip category (0 for small and 1 for large) nor nose category (0 for small and 1 for large) nor their actual dimensions were significant in these models. Dependent variables included were each significant at P < 0.05.