Cloud Radiation
densation nuclei counter. This instrument records the number of CCN active
at a single supersaturation (set at 0.33% for this study). The lowermost dotted
line is the large aerosol concentration (0.31.0 m) measured with a Particle
Measuring Systems passive cavity aerosol spectrometer probe (PCASP-100X).
The instrument provides a histogram of aerosol concentration in 15 size rang-
es. The concentration from each size range is totaled to provide the concentra-
tion reported in the figure.
Sampling began on day 208 with instruments running on a continuous
basis. The concentration of aerosols measured by all instruments decreased
sharply upon entering the ice. The concentration of CN, CCN (active at 1%
supersaturation) and CCN (active at 0.33% supersaturation) "track" each other
through the time series, with the PCASP-100X showing this trend but not as
dramatically as the other measurements. Generally CCN concentrations in
maritime air masses rarely exceed 100 cm3; however, concentrations above
100 cm3 were measured over a time of days in the remote Arctic Ocean (days
218224 and days 228232). These large CCN concentrations also accompan-
ied large CN concentrations, which in one in-
stance (day 224) exceeded 7000 cm3.
500
The concentrations of the larger aerosols,
CCN (1.0% S)
measured by the PCASP-100X and the CCN
CN (0.33% S)
400
active at 0.33% supersaturation, never exceed-
ed 100 cm3 while we were sampling in the
ice. The observations of the largest CN and
300
CCN (active at 1% supersaturation) concen-
trations correspond to the lowest observed con-
centrations of the large aerosol with the
200
PCASP-100X. This suggests that the elevated
CN concentrations may be due to a local pro-
100
duction mechanism. The reduction of the larg-
est aerosol removes a significant surface area
for the condensation of precursor gases. The
0
2
4
6
8
10
concentration of these gases increases until, by
Ice Coverage (tenths)
the process of gas-to-particle conversion, they
are converted into fine aerosol particles. Between days 218 and 224 the con- CCN concentration
centration of the finest aerosols are out of phase with the concentrations of the aonwo supersagurnst
tt
at a-
ti s plotted ai
largest aerosols; the peaks in concentration of one corresponds to the mini- ice coverage.
mums of the other. Although this scenario may not be the cause of the ob-
served concentrations, the high concentrations of the precursor gases neces-
sary have been recorded in the Arctic. The figure above shows the relationship
between ice coverage and CCN concentration, illustrating the possible pro-
duction of CCN from precursor gases. When the gas supply is limited by ice
cover, CCN concentration decreases. Regardless of the source, the particles are
present and are modifying the climate of the remote Arctic.
79
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