1.4x10^61.21.00.80.60.40.20d N/d logdp(cm-3)3 4 5 6 7 8 9
102Particle diameter, dp (nm)101102103104105106d N/d logdp(cm-3)4 5 6 7 8 9
d^10
p (nm)0 10 20 30 40
Appearance time (min)dact = 4.7 nma12345671023Activation diameter,dact(nm)1042 4 68
1052 4 68
1062[HNO 3 ] · [NH 3 ] (pptv^2 )-10o
C+5 oCb246(^108)
2
4
6
(^1008)
2
Saturation ratio of [HNO
] · [NH 3
] 3
2 3 4 5 6789
10
2 3
Particle diameter, dp (nm)
ds = 1.4 nm, -10 °C
ds = 1.4 nm, +5 °C
ds = 2.0 nm, -10 °C
ds = 2.0 nm, +5 °C
ds = 2.9 nm, -10 °C
ds = 2.9 nm, +5 °C
c
Extended Data Fig. 2 | Activation diameter of newly formed particles.
a, Determination of the activation diameter, dact, from a rapid growth event at
+5 °C, in the presence of nitric acid, ammonia and sulfuric acid. The solid
orange trace in the insert indicates the first size distribution curve that
exhibited a clear bimodal distribution, which appeared roughly 7 min after
nucleation. We define the activation diameter as the largest observed size of
the smaller mode. In this case, dact = 4.7 nm, which agrees well with the value
obtained from MABNAG simulations (roughly 4 nm) under the same conditions
as in Fig. 4. b, Activation diameter versus vapour product. Measured activation
diameters at a given temperature correlate inversely with the product of nitric
acid and ammonia vapours, in a log-log space. An amount of vapour product
that is approximately one order of magnitude higher is required for the same
dact at +5 °C than at −10 °C, because of the higher vapour pressure (faster
dissociation) of ammonium nitrate when it is warmer. c, Equilibrium particle
diameter (dp) at different saturation ratios of ammonium nitrate, calculated
according to nano-Köhler theory. Purple curves are for +5 °C and green curves
are for −10 °C (as throughout this work). The line type shows the diameter of the
seed particle (ds). The maximum of each curve corresponds to the activation
diameter (dact). A higher supersaturation is required for activation at lower
temperature.