1. Droplet Nuclei Measurements in VOCALS Intro and Preliminary Results
Counterflow Virtual Impactor (CVI)
Collects droplets while rejecting interstitial aerosols & vapor
Evaporates water so sample stream has non-volatile residual particles
Change minimum size (cut size) of drops by changing counterflow rate

2. Instruments Used for VOCALS Behind the CVI
3 instruments were part of basic CVI system for cloud LWC, drop residual number and size (Toohey)
3 additional instruments to measure chemical characteristics of droplet residual particles (collaborations)
Streaker
SEM
Aerosol Comp
Impactor
TEM
Additional Instruments
AMS
C, S, N mass
OPC
Residual
Nuclei Size
TDL
Liquid
Water Content
CN Counter
Nuclei Number
Basic System

3. R3 20 S Flight, Droplet Number Transition from Polluted to Clean Clouds and Back
75 West
85 West
75 West

4. CVI Residual Nuclei Size Distributions (uncorrected for CVI enhancement)
75 West
85 West
75 West
Near shore, there are more residual nuclei (more drops) & bigger nuclei
Offshore, nuclei are smaller: less pollution, more removal of aerosol through precipitation scavenging.
(Not shown): Residual nuclei are larger than ambient aerosol:
nucleation scavenging, in-cloud coalescence & chemical rxns.

5. Which Nuclei form Largest Drops
Which Nuclei form Largest Drops? Important for understanding droplet activation and drizzle formation
>7 m
>11 m
>14 m
>16 m
>8 µm
filter change
filter change
Largest nuclei form largest drops through condensational growth
Largest drops also may contain >one nuclei (coalescence)—clean clouds
Composition is also important in droplet activation and indirect effects on clouds