Table 4.

Comparison of coefficient values for studies that correlate N_d to ${\text{SO}}_4^{2-}$ (total or non-sea-salt). The coefficients correspond to a linear model of the form $\text{log}\left(N_{\text{d}}\right)=a_0+a_1\text{ log}\left({\text{SO}}_4^{2-}\right)$.

Reference	a0	a1	${\text{SO}}_4^{2-}$	R2	Cloud type
Leaitch et al. (1992)a	1.95	0.257	Tot	0.3	Continental stratocumulus
	2.33	0.186	Tot	0.49	Continental cumulus
Novakov et al. (1994)	2.323	0.091	NSS	0.50b	Marine stratocumulus
	2.43	−0.056	NSS	0.03	Marine cumulus
Van Dingenen et al. (1995)c	2.33	0.4	NSS	0.42	All cloud types combined
Boucher and Lohmann (1995)c	2.24	0.257	NSS	d	Continental stratus
	2.54	0.186	NSS	d	Continental cumulus
	2.06	0.48	NSS	d	Marine
	2.21	0.41	NSS	d	All cloud types combined
Saxena and Menon (1999)	0.67	0.66	Tot	d	Continental orographic clouds
Lowenthal et al. (2004)	2.32	0.74	NSS	0.82	Marine
	2.38	0.49	NSS	0.66	Continental
	2.39	0.5	NSS	0.81	Combined
McCoy et al. (2017)	2.11	0.41	NSS	0.36	Marine stratocumulus

^aThe units of ${\text{SO}}_4^{2-}$ for this regression are nanoequivalents per cubic meter (nEq m⁻³). All other studies report ${\text{SO}}_4^{2-}$ in units of micrograms per cubic meter (μg m⁻³). However, the value of the slope (a₁) is not affected by the units of concentration.

^bThe R² has a p > 0.05 due to having few data points.

^cThese regressions were made using data compiled from several studies and assume that N_ccn ≈ N_d.

^dStudy does not report R².