SMPS

Inhalt Atmosphärisches Aerosol Messgeräte: SMPS, DMA & CPC, DMPS, PM10 oh je oh je Datenauswertung Ausblick: FOX I will start with a short outline I will first give an introduction….

Atmosphärisches Aerosol I will start with a short outline I will first give an introduction….

Atmosphärisches Aerosol - The chosen location will be closed to the lake of Zuerich on the „Albis-ridge“ - 735 above mean sey level - Anthropogenic effect: highway and incineration plant

Aerosole - The chosen location will be closed to the lake of Zuerich on the „Albis-ridge“ - 735 above mean sey level - Anthropogenic effect: highway and incineration plant

Wie gross sind Aerosole?

Typical Aerosol Particle Size Ranges Cloud droplets: ~ 4 - 100µm Fog droplets: ~ 5 - 20µm From Friedlander: Smoke, Dust and Haze

Grössenverteilung - The chosen location will be closed to the lake of Zuerich on the „Albis-ridge“ - 735 above mean sey level - Anthropogenic effect: highway and incineration plant

Geographische Variation - The chosen location will be closed to the lake of Zuerich on the „Albis-ridge“ - 735 above mean sey level - Anthropogenic effect: highway and incineration plant

Messinstrumente SMPS, DMA & CPC, DMPS, PM10 oh je oh je I will start with a short outline I will first give an introduction….

In-situ Grössen & Anzahlmessung How do we measure particle number and particle size ? Following techniques have been used to count particles in the past: microscope (particles collected on a plate) picture (cloud chamber) single particle in a continuous flow (most popular in situ aerosol instrument ) http://www.knovel.com/knovel2/Toc.jsp?BookID=1080 Link for Aerosol Measurement - Principles, Techniques, and Applications (2nd Edition) Edited by: Baron, Paul A.; Willeke, Klaus © 2001 John Wiley & Sons In-situ: man misst wo die Partikel sind Ex-situ: man misst von ausserhalb (z.B. Radar)

1. Anzahl: Condensation Particle Counter Important instruments in aerosol technology are Condensation Particle Counters (CPC). They are used to measure the particle number concentration down to the nanometer size range. The particles are enlarged due to supersaturation and a subsequent condensation of a condensable gas (normally Butanol, now also water!). The particles reach a size at which they can be optically detected. The number concentration is measured for all particle larger than the lower detection diameter.

1. Anzahl: Condensation Particle Counter CPCs are used to measure the number concentration in the submicrometer size range. The lower detection diameter is determined by: the Kelvin diameter (supersaturation) diffusion coefficient of the condensable gas the particle material The upper and lower detection limits are specific for each CPC type.

1.Continuous Flow CPC Modern CPCs operate with continuous aerosol flows and are able to count each single particle. Model TSI 3010, 3760, 3762,…: Principal: continuous flow, single particle counting Lower detection Buthanol: 10 nm (Model 3025: 3 nm,) diameter: Water CPC: 5nm Upper detection diameter: ca. 3000nm Concentration range: 0-10,000 cm-3 (Model 3025: 0-105 cm-3) Accuracy: 10% compared to a reference instrument Aerosol flow: 1.0 l/min

1. Schematic sketch of the CPC models TSI 3010 (also 3760, 3762) Functioning: The aerosol flow is saturated with butanol in a slightly heated saturator. The the temperature of the butanol-aerosol mixture is decreased by 17-27°C in the condenser of the CPC. Here, the butanol become supersaturated and condenses onto the particles. The particles grow to droplets of several µm in diameter. The droplet flow is focused in a nozzle and introduced into a counting optic. The droplets pass a laser beam, and each single particle creates a light pulse. Pulses with an amplitude above a certain threshold are counted. The particle number concentration can be calculated by knowing the aerosol flow rate.

1. Functioning The aerosol flow is saturated with butanol in a slightly heated saturator. The the temperature of the butanol-aerosol mixture is decreased by 17-27°C in the condenser of the CPC. Here, the butanol become supersaturated and condenses onto the particles. The particles grow to droplets of several µm in diameter. The droplet flow is focused in a nozzle and introduced into a counting optic. The droplets pass a laser beam, and each single particle creates a light pulse. Pulses with an amplitude above a certain threshold are counted. The particle number concentration can be calculated by knowing the aerosol flow rate (critical orifice).

1. CPC Data Teamviewer: 153 161 526 8814

Wie misst man die Grösse eines Aerosols? - The chosen location will be closed to the lake of Zuerich on the „Albis-ridge“ - 735 above mean sey level - Anthropogenic effect: highway and incineration plant Unser Massband: Differential Mobility Analyser

Was ist die Grösse eines Aerosols? Apfel: Durchmesser Soot: ??? - The chosen location will be closed to the lake of Zuerich on the „Albis-ridge“ - 735 above mean sey level - Anthropogenic effect: highway and incineration plant

Was ist die Grösse eines Aerosols? - The chosen location will be closed to the lake of Zuerich on the „Albis-ridge“ - 735 above mean sey level - Anthropogenic effect: highway and incineration plant Partikel mit gleicher electrical mobility

Was ist die Grösse eines Aerosols? APS SMPS - The chosen location will be closed to the lake of Zuerich on the „Albis-ridge“ - 735 above mean sey level - Anthropogenic effect: highway and incineration plant Partikel mit gleicher electrical mobility

2. Particle Size - Differential Mobility Analyzer  

2.1 Electric Mobility Electrically charged particles move in an electric field according to their electrical mobility. The electrical mobility ZP of a particle with a certain electric charge is defined to (given in [cm2/Vs]): With ve derived analog to the sedimentation velocity The electrical mobility depends mainly on the particle size and electrical charge. The smaller the particle the higher is the electrical mobility. The higher the electrical charge the higher is the electrical mobility. n = number of charges e = elementary charge B = particle mobility (“velocity per unit force”)  

2. 2 Funktionsweise Assumption: All particles carry only one electrical charge. The electrical mobility is than only a function of the particle size in case of constant temperature and pressure. Example: An electrically charged polydisperse aerosol is led through a plate capacitor. Electrically charged particles are separated and deposited according their size.  

2. Particle Size - Differential Mobility Analyzer Plate mobility analyzer: aerosol d sheath air  

2.3 Theory of a plate mobility analyzer:  The most simple mobility analyzer is a plate capacitor.   A laminar particle-free sheath air flow Qsh is led through the capacitor (x-direction). An electric field is put between the plates (z-direction). The aerosol flow QA (x-direction) is fed into the capacitor close to one plate.   The total volume flow is  The particle velocity in x-direction is given to: The particle velocity in z-direction is defined to:

   with w = width of the capacitor d = distance between plates The electrical mobility for a certain deposition place is given to: The voltage to select a certain mobility can be calculated by:

2.4 Theory of cylindrical mobility analyzer:

2.4 Theory of cylindrical mobility analyzer: Folie neu drucken 2.4 Theory of cylindrical mobility analyzer:  : The theory is analogous to the plate capacitor. The total flow is given to:  The particle velocity in x-direction is given to:  The radial velocity due to the electric field is described to:  with 

  The electrical mobility for a certain deposition place is given to: The voltage to select a certain electrical mobility incl. the electrical mobility from Stokes‘ law can be calculated to:  The particle size for a certain deposition place and voltage cannot be analytically solved:

2. Differential Mobility Analyzer   The voltage to select a certain electrical mobility incl. the electrical mobility from Stokes‘ law can be calculated to: e = elemental charge 1,602·10-19 As n = number of charges The particle size for a certain deposition place is: ∆DP= 1 nm or DP =10nm ± 0.5nm

2. Differential Mobility Analyzer Aerosol particles can be classified due to their electrical mobility in a DMA. A small volume flow Qs with particles of a defined mobility is taken out of the DMA through a slit at the end of the inner rod.   The mean mobility of these particles can be calculated to: The ideal width of the mobility bin is described to: for  QA=QS and QA =1/10 QSh

2. Differential Mobility Analyzer Example: DP= 10 nm with ZP = 2.078.10-2 cm/Vs and ∆ ZP = 4.156·10-3 cm/Vs ∆DP= 1 nm or DP =10nm ± 0.5nm   the size resolution is excellent! The size resolution depends mainly on the ratio of the volume flow rates QA/QSh. The greater the ratio, the better becomes the size resolution.  

2. 5 Transfer function   The transfer probability over the mobility bin is not unity. The DMA-transfer function depends on the particle size and sample flow ratio.   Example: QA= Qs The transfer function has the form of a symmetric triangle. The transfer probability of the mean electrical mobility is unity. The transfer probability of the upper and lower limit of the mobility bin is Zero. For QA>QS und QA<QS, the transfer function becomes asymmetric. This cases are not discussed, because they are not the standard applications.

2. 5 Transfer function Ideal transfer function:

2. 5 Transfer function Real transfer function: In reality, the DMA transfer function depends also on the DMA-design. The transfer function becomes a function of the particle diameter. The reasons are: Diffusion broadening for ultrafine particles Particle losses in the aerosol inlet and outlet of the DMA. The transfer function becomes broader and the maximum transfer probability decreases. 

2.6 Generator for Monodisperse Particles The DMA can select a quasi monodisperse aerosol from a polydisperse aerosol population.   A generator for monodisperse aerosol particles consists of: a polydisperse aerosol generator (atomizer, tube furnace) a bipolar diffusion charger a DMA  The monodisperse aerosol with the size DP1 can however contain larger particles with the same electrical mobility carrying more elementary charge units. Example: DP1 = 100 nm (singly charged) DP2 = 152 nm (doubly charged) DP3 = 196 nm (triply charged)

3. DMA + CPC How do we measure particle number and particle size ? http://www.knovel.com/knovel2/Toc.jsp?BookID=1080 Link for Aerosol Measurement - Principles, Techniques, and Applications (2nd Edition) Edited by: Baron, Paul A.; Willeke, Klaus © 2001 John Wiley & Sons How do we measure particle number and particle size ? Combination of DMA+CPC (most common application for atmospheric measurements)

Electrical Mobility Spectrometer The DMA can be used to measure the number size distribution of a polydisperse aerosol. There exist two different principles: 1. The voltage is increased stepwise (DMPS) 2.The voltage is continuously increased (SMPS) A electrical mobility spectrometer consists of: a bipolar diffusion charger a DMA a CPC

Electrical Mobility Spectrometer A electrical mobility spectrometer can measure a size distribution only for a certain size range. This size range depends on the DMA-geometry and the sheath air flow rate. Longer DMA  larger particle diameter Higher sheath air flow rate  smaller particle diameter

Computer inversion routine: The computer inversion routine calculates the number size distribution out of the mobility distribution. For a complete inversion routine must be known: The mobility distribution The bipolar charge distribution The size dependent DMA transfer function The CPC detection efficiency curve

Differential Mobility Particle Sizer (DMPS) A pre-impactor removes all particles larger than the upper diameter of the size range to be measured   The particles are brought in the bipolar charge equilibrium in the bipolar diffusion charger. A computer program sets stepwise the voltage for each selected mobility bin. After a certain waiting time, the CPC measures the number concentration for each mobility bin. The result is a mobility distribution. The number size distribution must be calculated from the mobility distribution by a computer inversion routine.

Scanning Mobility Particle Sizer (SMPS) The design of the system is identical to the DMPS. The difference lies in the measurement principle. The voltage is continuously increased. There is no waiting time any longer. The particle concentration is measured as function of time. The relationship between electrical mobility and time (time between DMA entrance and CPC detection) must be determined for each SMPS system. The results is again a mobility distribution. The number size distribution must be calculated from the mobility distribution by a computer inversion routine.

Scanning Mobility Particle Sizer (SMPS) Teamviewer 498 662 983 2272

Messinstrumente SMPS, CPC & DMA, DMPS & PM10 ist jetzt klar? I will start with a short outline I will first give an introduction….

Datenauswertung I will start with a short outline I will first give an introduction….

Scanning Mobility Particle Sizer (SMPS) Output: APS Average config Contour diagnostics integral Inverted Raw raw long

Particle Size Distributions

Particle Size Distributions

Particle Size Distributions

Area, Volume-Mass Distributions Heterogeneous and multiphase reaction rates depend on surface area or volume, respectively. Gravitational settling rates depend on mass and air quality standards are mass-based. Assuming spherical geometry and dDp0 dS(Dp) = Dp2n(Dp)dDp dV(Dp) = (/6)Dp3n(Dp)dDp

Typical Number Distribution for Urban Aerosols Solid line: what would be observed, composed of 3 modes Dotted/Dashed lines: Two common parameterizations Junge Distribution (dashed line) is a power law. Has some useful properties but requires care. Log-Normal distribution (dotted line) is most often used (see Pruppacher-Klett, chapter 8.2.9. for mathematical formulation)

Ausblick: FOX I will start with a short outline I will first give an introduction….

Why are we interested in fog? Aerosol-cloud interaction is poorly known, especially the anthropogenic effect In our group we do modelling & lab experiments, but it is essentiel that we also measure in the field (comparison to modelled data & lab data) So the goal of my talk today will be to convince you that measuring in the fog layer in could indeed help to increase our understanding of the anthropogenic role in the aerosol-cloud interaction Indirect effect of aerosols on climate poorly known – especially the anthropogenic effect

Fog in Switzerland Zürich From Jordi 2004 In Wintertimes a persitent low stratus layer can form above the swiss midlands as you can see on this satelite picture From Jordi 2004

Fog in Switzerland Droplets: 5-20mm (Wanner, 1979) Droplets Image: courtesy of Hanna Herich (adapted) Droplets: 5-20mm (Wanner, 1979) Having a closer look to fog: it consists of droplets and interstital aerosols Droplets can only form due to the presence of aerosols that serve as condensation nuclei (cloud residuals) -> Fog is „static“ WHY DID I SAY THAT THIS IS A GOOD SYSTEM TO MEASURE ANTHROPOGENIC EFFECTS? Why is this such an interesting topic to study Aerosols needed for cloud formation have natural and anthropogenic sources. By measuring aerosol properties and cloud droplets one can get new inside knowlegde into Aerosol cloud interaction and the anthropogenic effect on this system Droplets Total aerosol Cloud residuals Interstitial aerosols

? ? Fog in Switzerland Weekly & Daily cycle Industrial snow Image: courtesy of Hanna Herich (adapted) Droplets: 5-20mm (Wanner, 1979) Droplets: Diurnal / weekly cycle in the droplet concentration? Total aerosol: Physical properties CCN activation Cloud residuals: Anthropogenic markers (metals & carbon) ? ? So coming back to the fog layer, I will be interested in 3 different things: Droplets Physical properties of the total aerosol Weekly & Daily cycle Industrial snow

FOg Characterisation EXperiment Image: courtesy of Hanna Herich (adapted) Droplets: 5-20mm (Wanner, 1979) Droplets: Diurnal / weekly cycle in the droplet concentration? Fog Monitor Total aerosol: Physical properties CCN activation SMPS & CCNC Cloud residuals: Anthropogenic markers (metals & carbon) CVI /Massspectrometer ? ? How to measure Weekly & Daily cycle Industrial snow Additional: PM1, PM10 & gas phase measurements, anemometer (wind), ceilometer

Fog in Switzerland We needed to find an appropriate location where we can measure inside the fog Using frequency maps from Bachman and Bendix Satellite observations: distribution & frequency maps (Bachman & Bendix, 1993; Jordi, 2004)

FOX garbage incineration plant AMSL - The chosen location will be closed to the lake of Zuerich on the „Albis-ridge“ - 735 above mean sey level Anthropogenic effect: highway and incineration plant Criteria -Fog -Emissions -reachable -Power supply

Our Trailer CVI inlet: cloud residuals Total Inlet: CVI Dryer Mass Condensation Spectrometer Particle (chemical Counter Analysis) Total Inlet: Scanning Cloud Mobility Condensation Particle Nuclei Sizer Counter (Aerosol size distribution) Dryer CVI Dryer - The chosen location will be closed to the lake of Zuerich on the „Albis-ridge“ - 735 above mean sey level - Anthropogenic effect: highway and incineration plant Droplet measurements: Fog Monitor

I will start with a short outline I will first give an introduction….

Measuring Aerosols: Part 1: How do we measure particle number? I will start with a short outline I will first give an introduction….

How do we measure particle number? Following techniques have been used to count particles in the past: microscope (particles collected on a plate) picture (cloud chamber) single particle in a continuous flow (most popular in situ aerosol instrument ) http://www.knovel.com/knovel2/Toc.jsp?BookID=1080 Link for Aerosol Measurement - Principles, Techniques, and Applications (2nd Edition) Edited by: Baron, Paul A.; Willeke, Klaus © 2001 John Wiley & Sons

Condensation Particle Counter… ... Is an important instruments in aerosol technology …Is used to measure the particle number concentration down to the nanometer size range Detection in 2 steps: 1. The particles are enlarged due to supersaturation and a subsequent condensation of a condensable gas 2. The particles reach a size at which they can be optically detected.

Schematic sketch of the CPC models TSI 3010 (also 3760, 3762) Functioning: The aerosol flow is saturated with butanol in a slightly heated saturator. The the temperature of the butanol-aerosol mixture is decreased by 17-27°C in the condenser of the CPC. Here, the butanol become supersaturated and condenses onto the particles. The particles grow to droplets of several µm in diameter. The droplet flow is focused in a nozzle and introduced into a counting optic. The droplets pass a laser beam, and each single particle creates a light pulse. Pulses with an amplitude above a certain threshold are counted. The particle number concentration can be calculated by knowing the aerosol flow rate.

1. Functioning The aerosol flow is saturated with butanol in a slightly heated saturator. The the temperature of the butanol-aerosol mixture is decreased by 17-27°C in the condenser of the CPC. Here, the butanol become supersaturated and condenses onto the particles. The particles grow to droplets of several µm in diameter. The droplet flow is focused in a nozzle and introduced into a counting optic. The droplets pass a laser beam, and each single particle creates a light pulse. Pulses with an amplitude above a certain threshold are counted. The particle number concentration can be calculated by knowing the aerosol flow rate (critical orifice).

CPC - facts Modern CPCs operate with continuous aerosol flows and are able to count each single particle. Model TSI 3010, 3760, 3762,…: Principal: continuous flow, single particle counting Lower detection Buthanol: 10 nm (Model 3025: 3 nm,) diameter: Water CPC: 5nm Upper detection diameter: ca. 3000nm Concentration range: 0-10,000 cm-3 (Model 3025: 0-105 cm-3) Accuracy: 10% compared to a reference instrument Aerosol flow: 1.0 l/min

CPC: detection limits The lower detection diameter is determined by: the Kelvin diameter (supersaturation) diffusion coefficient of the condensable gas the particle material The upper and lower detection limits are specific for each CPC type.

I will start with a short outline I will first give an introduction….

1. CPC Data Teamviewer: 153 161 526 8814

A.2 Aerodynamic Particle Sizer (APS) The APS measures the aerodynamic particle diameter and can thus determine the aerodynamic particle size distribution. Aerodynamic diameter: The aerodynamic particle diameter is defined as: „Diameter of a spherical particle with the density of One and the same sedimentation velocity of the measured particle".  = dynamic shape factor 0 = 1g/cm3, e.g. water The Stokes-Diameter and the Aerodynamic Diameter are so-called equivalent diameters.

Specification of the APS: The APS determines the aerodynamic number size distribution with a high time resolution. The aerodynamic particle size range of the APS model TSI 3321 is between 0.5 and 20 µm. Solid and non-volatile particles can be measured.

Schematic of the APS: Acceleration nozzle: The acceleration nozzle consists of an inner and out nozzle. The inner nozzle focuses the aerosol flow. The aerosol flow is then surrounded by the sheath air flow. The entire flow is then accelerated through the outer nozzle. The total flow rate of 5 l/min consists of 1 l/min aerosol flow and 4 l/min particle-free sheath air. The velocity of the aerosol flow in the center is assumed to be constant. Due to inertia, particles with a large aerodynamic diameter cannot follow the acceleration. This means that particle with different aerodynamic diameters have different velocities directly behind the nozzle (calibrated instrument !). The laser anemometer measures the time-of-flight between two laser beams. Laser anemometer The laser beams are positioned directly behind the outer nozzle. Particles passing the laser beams emit two light pulses. The time difference between the two pulse maxima is the time-of-flight. The time-of-flight is a measure for the aerodynamic particle diameter. The relation between time-of-flight and aerodynamic particle size must be calibrated for each device. The main part of the APS are the acceleration nozzle and the laser anemometer.

Acceleration nozzle: The acceleration nozzle consists of an inner and out nozzle. The inner nozzle focuses the aerosol flow. The aerosol flow is then surrounded by the sheath air flow. The entire flow is then accelerated through the outer nozzle. The total flow rate of 5 l/min consists of 1 l/min aerosol flow and 4 l/min particle-free sheath air. The velocity of the aerosol flow in the center is assumed to be constant. Due to inertia, particles with a large aerodynamic diameter cannot follow the acceleration. This means that particle with different aerodynamic diameters have different velocities directly behind the nozzle (calibrated instrument !).

Laser anemometer: The laser anemometer measures the time-of-flight between two laser beams. The laser beams are positioned directly behind the outer nozzle. Particles passing the laser beams emit two light pulses. The time difference between the two pulse maxima is the time-of-flight. The time-of-flight is a measure for the aerodynamic particle diameter. The relation between time-of-flight and aerodynamic particle size must be calibrated for each device.

Optical measurements: Beside the determination of the aerodynamic particle size, the signal can also be taken to determine the optical diameter (see also Optical Particle Counter OPC). Each particle is classified in relation to the refractive index of latex spheres.

B.3 Applications of DMPS-Systems B.3.1 Twin Differential Mobility Particle Sizer (TDMPS) A combination of two electrical mobility spectrometers allows to measure the size distribution of the entire submicrometer size range.

B.3.2 Tandem Differential Mobility Analyzer (TDMA)   A TDMA is a system where two DMAs are applied in series. A TDMA can measure the mixing state of a defined particle size in terms of a certain aerosol parameter. The first DMA selects a monodisperse aerosol out of the entire aerosol population. The monodisperse aerosol is modified in a conditioner The new size spectrum is determined with the second DMA Applications: Bipolar charge distribution Hygroscopicity Volatility

Hygroscopicity-Tandem-Differential-Mobility-Analyzer (HTDMA)

Examples of HTDMA measurement Particle Number Concentration 1/cm3 Particle Diameter (nm) 1 10 100 1000 107 105 103 101 10000 Sulfuric Acid Organic Nitrate Carbonaceous Sulfate Sea Salt Mineral Wet Dp Dry Dp Elevated RH