GRIMM Aerosol Spectrometer and Dust Monitors. Measuring principle

Transcription

1 Grimm Aerosol-Technik GRIMM Aerosol Spectrometer and Dust Monitors Measuring principle Eng. Wolfgang Brunnhuber 1 Agenda Part A physical background general principles of optical particle detection Part B Nanoparticles counting and sizing This presentation was brought to you by Mazoon Environmental and Technological Services LLC info@mets-oman.com 2 11 May

2 physical background: Interaction of radiation and aerosol particles a = p d p /l with d p = particle diameter and l = incident wavelength note: p d p = particle circumference, for spherical particles The interaction between incident light and a particle (solid, droplet and or gas molecules!) is strongly dependent on the particles size and the wavelength. To show this dependency, the parameter a is used. [Seinfeld & Pandis, 1998] 4 physical background: dependency of particle size and wavelength on scattering For particle sizes much smaller than the incident wavelength (a << 1) RAYLEIGH-scattering: the oscillating electric field of the light waves induce an oscillating dipole in the particle, causing symmetrical scattering (in forward and backward directions). The Intensity of the scattered light is proportional to the sixth power of particle diameter (I ~ d p 6 ) Example: Sunlight hits gas molecules in the atmosphere, blue sky effect! a = p d p /l with d p = particle diameter; and l incident wavelength note: p d p = particle circumference, for spherical particles [Baron & Willeke, 2001] 5 11 May

3 physical background: dependency of particle size and wavelength on scattering For particle sizes in the size range as the incident wavelengt (depending on the light source! say 0.1µm-1µm) MIE-scattering: strong interaction between the particle and the incident beam, depending although on particle refractive index. No simple relation between scattered intensity and particle diameter (Mie-programs, spherical particles) Gustav Adolf Feodor Wilhelm Ludwig Mie * a = p d p /l with d p = particle diameter; and l incident wavelength note: p d p = particle circumference, for spherical particles [Baron & Willeke, 2001] 6 physical background: dependency of particle size and wavelength on scattering For particle sizes much bigger than the incident wavelength (a >> 1) GEOMETRIC OPTICS: light rays hitting the particle lead to reflection, refraction and absorption, rays passing the particles edge give rise to diffraction. The scattered intensity is proportional to the particle crosssectional area (I ~ d p 2 ) and not strongly dependent on shape or particle composition Example: Sunlight hits water droplets in clouds, they appear white! a = p d p /l with d p = particle diameter; and l incident wavelength note: p d p = particle circumference, for spherical particles [Baron & Willeke, 2001] 7 11 May

4 physical background: scattering intensity vs. particle size Geometric Optic Defines the maximum particle size you are able to detect Mie Rayleigh Defines the minimum particle size you are able to detect. Electronical background noise due to scattered light from gas molecules or particle scattering = particle circumference incident wavelength [Baron & Willeke, 2001] 8 physical background: single particle light scattering, scattering intensity polar diagram BACKWARD SCATTERED Scattered intensity I is a function of a = size parameter = p d p /l with d p = particle diameter, l = incident wavelength m = refractive index = n -i with n = real part (scattering), i = imaginary part (absorption) Q = scattering angle while ~0 = backward scattered, ~180 = forward scattered [Baron & Willeke, 2001, Haller 1999] 9 11 May

5 physical background: single particle light scattering, scattering intensity 3D plot calculation of the scattering intensity for a spherical particle, d p = 2µm, incident light: laser, l = 633nm Figure from: René Michels, ILM Uni-Ulm 10 principles of optical particle detection: components, function and design component Sample air inlet Sample air pump Light source Beam optic Light trap Detection optic Detector Signal processing & data processing function/design reproducibility, rh, isokinetic / various flow rate, concentration, statistic / various signal / laser, diode laser, white light well defined optical volume / various avoiding noise / various known aperture / backward, forward, 90 optical or aerodynamic focusing scattering light / photo diode, multiplier rapid count processing and accurate size classification / various All components together determine the spectrometers counting efficiency (coincidence concentration) and sizing accuracy (particle size resolution) May

6 principles of particle detection Nephelometer aerosol particles y detection volume x Sample in Light source Detector Signal by a group of particles! y 12 principles of particle detection Spectrometer e.g. 90 detection aerosol particles aerosol focusing detection volume 90 y z x Sample in Light source y Detector Light trap GRIMM can do!! Signal by a single particle! May

7 physical background: single particle light scattering, Grimm spectrometer principle 14 principles of particle detection Dual method, spectrometer and gravimetric filter (Grimm) Light scattering in real time for particle number concentration and size distribution Particle sampling on filter for gravimetric use to determine specific particle mass aerosol focusing Dual technology in one device! Grimm patent! (1) filter chamber, open with 49mm PTFE filter (2) May

8 specification: grimm spectrometer Specifications Dust range [µg/m³] Size Range [µm] Size channels [µm] Sample air Particle counting Battery duration Weight / Dimensions Data output via Windows software #1.108 # > > > >32 15 channels counts 31 channels counts 16 channels mass 32 channels mass (0.23)/0.3/0.4/0.5/0.65/ (0.23)/0.25/0.28/0.3/0.35/0.4/0.45/ 0.8/1/1.6/2/3/4/5/7.5/10/ 0.5/0.58/0.65/0.7/0.8/1/1.3/1.6/2/ 15/20 2.5/3/3.5/4/5/6.5/7.5/8.5/10/12.5/ 15/17.5/20/25/30/ l/min up to P/l up to 8h 2.5 kg with battery / 24 x 12 x 6 cm Particle concentration in particles/litre, for all size channels or Particle mass in µg/m³, for all size channels Particle mass fractions in µg/m³, simultaneously according to EN 481 occupational (inhalable, thoracic, respirable) and EPA environmental (PM 10, PM 2.5, PM 1 ) May