construction and characterisation of a particle magnifier helene holmgren
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Construction and Characterisation of a Particle Magnifier
Helene Holmgren
Outline
• Background
• Condensation Particle Counter – CPC
• Pulse Height Analysis - PHA
• Particle Magnifier
• Future Applications
• Take Home Messages
Background
• Particle formation and growth
• Clusters - particle
• Nanoparticles–Too small to scatter enough light to be detected by
optical methods
–Too small to carry significant charge to be classified according to electrical mobility
–Diffusion losses
Condensation Particle Counter
• 2.5 – 1000 nm (TSI)
• <10,000,000 particles cm-3 (TSI)
• Measures particle number concentrations, but all information regarding size is lost
Condensation Particle Counter
• Heated saturator–Vaporisation of
working medium
• Cooled condenser–Supersaturation
–Condensation and growth
• Optical detector–Light scattering
Condensation Particle Counter
• S saturation ratio
• P actual vapour partial-pressure (Pa)
• P saturation vapour pressure (Pa)
• g surface tension (N m-1)
• M molecular weight (kg mol-1)
• r density (kg m-3)
• R universal gas constant (J K-1 mol-1)
• T absolute temp (K)
• d Kelvin diameter (m)
rRTd
gM
P
PS
s
4exp
Pulse Height Analysis
• Measures pulse heights produced when particles pass laser beam
• Particles <15 nm (Saros et. al 1996)
–Pulse height increases with particle size
• Particles > 15 nm (Saros et. al 1996)
–All particles grow to the same size
Particle Magnifier
• Detect, count AND size nanoparticles
• Push size detection limit downwards–Optimise saturation and cooling systems
–Find the most favourable working medium
• Minimise diffusion losses– Instrument design
condenser
particles
saturator
optical detection
Particle Magnifier
Particle Magnifier
• Grimm Dust Monitor
• IR-laser
• Light-scattering
• Pulse Height Analysis
Particle MagnifierGrim m
0200400600800
100012001400160018002000
particle diam eter (µm )
par
ticl
es/li
tre
ΔT = 20 K
0
20000
40000
60000
80000
100000
120000
140000
160000
particle diam eter (µm )
par
ticl
es/li
tre
ΔT = 22 K
0
20000
40000
60000
80000
100000
120000
140000
160000
particle diam eter (µm )
par
ticl
es/li
tre
ΔT = 24 K
0
20000
40000
60000
80000
100000
120000
140000
160000
particle diam eter (µm )
par
ticl
es/li
tre
Future Applications
• Field measurements–SOA formation
–Terpenes emitted from vegetation
• Laboratory studies–SOA formation
–Connect to laminar flow tube (Emanuelsson)
Take Home Messages
• It is possible to obtain number-size distributions of nanoparticles by combining the principles of CPCs with PHA technique
• Particles <10 nm are activated at different sites in the condenser, and grow to different sizes
• Particles >10 nm are activated near the entrance of the condenser, and grow to the same size
References
• Saros, M., et al., Ultrafine aerosol measurement using a condensation nucleus counter with pulse height analysis. Aerosol Science and Technology, 1996. 25(2): p. 200-213.