Genetic Algorithm Approach to Particle Identification by Light Scattering

Hodgson, Richard

doi:10.1006/jcis.2000.6989

Cited by 20 publications

(16 citation statements)

References 17 publications

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“…Each search ran for three generations and had a mutation factor of 0.9. A population size of 50 is usually sufficient, however, the larger population ensures that the solution converges and that the highly complex solution space [ Hodgson , 2000] is thoroughly searched. The retrieved m r of each of these six searches varied less than 1% from the average GA‐determined refractive index of 1.48.…”

Section: Resultsmentioning

confidence: 99%

Real refractive indices of α‐ and β‐pinene and toluene secondary organic aerosols generated from ozonolysis and photo‐oxidation

2010

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[1] The refractive index is the fundamental property controlling aerosol optical properties. Secondary organic aerosol (SOA) real refractive indices (m r ) were derived from polar nephelometer measurements using parallel and perpendicular polarized 670 nm light, using a genetic algorithm method with Mie-Lorenz scattering theory and measured particle size distributions. The absolute error associated with the m r retrieval is ±0.03, and the instrument has sufficient sensitivity to achieve reliable retrievals for particles larger than about 200 nm. SOA generated by oxidizing a-pinene, b-pinene, and toluene with ozone and NO x /sunlight are explored. Retrieved refractive indices for the SOA vary between 1.38 and 1.61, depending on several factors. For a-and b-pinene ozonolysis, SOA m r ranges from 1.4 to 1.5 and, within the resolution of our method and bounds of our experiments, is not affected by the addition of an OH scavenger, and is only slightly dependent on the aerosol mass concentration. For photochemically generated SOA, m r generally increases as experiments progress, ranging from about 1.4 to 1.53 for a-pinene, 1.38 to 1.53 for b-pinene, and 1.4 to 1.6 for toluene. The pinene SOA m r appear to decrease somewhat toward the end of the experiments. Aspects of the data suggest aerosol mass concentration, oxidation chemistry, temperature, and aerosol aging may all influence the refractive index. There is more work to be done before recommendations can be made for atmospheric applications, but our calculations of the resulting asymmetry parameter indicate that a single value for SOA refractive index will not be sufficient to accurately model radiative transfer.Citation: Kim, H., B. Barkey, and S. E. Paulson (2010), Real refractive indices of a-and b-pinene and toluene secondary organic aerosols generated from ozonolysis and photo-oxidation,

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Section: Resultsmentioning

confidence: 99%

Real refractive indices of α‐ and β‐pinene and toluene secondary organic aerosols generated from ozonolysis and photo‐oxidation

2010

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“…Because it is a directed search method, it has the advantage of computational efficiency, and as it is not an analytical inversion, scattering solutions based on non-spherical shapes can be readily adapted. Hodgson (2000) has shown that the GA method is very effective in retrieving the correct solution from the many possible minima in the highly convoluted solution space of a similar problem. There are other possible optimization or search methods, i.e., lookup table methods or simulated annealing, but we chose the GA as we have experience with the GA software library used in this study and because our goal is not an examination of the methods, but in the result of the retrieval.…”

Section: Introductionmentioning

confidence: 99%

Genetic Algorithm Inversion of Dual Polarization Polar Nephelometer Data to Determine Aerosol Refractive Index

Barkey

Paulson

Chung

2007

Aerosol Science and Technology

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A polar nephelometer that measures the light scattered into a two dimensional plane by a stream of aerosols that intersect a 350 milliwatt diode laser beam with a wavelength of 670 nm is described. A half wave plate is used to orient the laser light both parallel and perpendicular to the measurement plane. This scattering information combined with simultaneously measured size distribution information is used to determine the real (m r ) refractive index of the aerosols using a Genetic Algorithm search method. Errors in the retrieved m r based on noise in the scattering measurement as well as uncertainties in the size distribution measurement are examined. The m r of polystyrene latex spheres and ammonium sulfate droplets are determined and match expectations within experimental uncertainties using Mie-Lorenz theory. The angular scattering properties of spherical secondary organic aerosols generated by oxidizing α-pinene do not follow this theory and calls into question the inferred m r .

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“…We have developed a genetic algorithm (GA) method to determine the real refractive index (GA m r ), the mean diameter (GA E(x)) and standard deviation (GA SD), assuming a lognormal distribution, from angular scattering measurements made with a 21 channel, dual polarization polar nephelometer (PN) (Barkey et al 2007). The GA method is particularly useful due to the highly irregular solution space of the scattering inversion problem (Hodgson 2000) and because the GA method is an optimization scheme, and not an analytical inversion, an examination of the problem to ensure closure, i.e., to ensure that the problem has a meaningful result is not necessary. Instead, as discussed in this paper, the convergence behavior of each problem is used to determine the soundness of the problem.…”

Section: Introductionmentioning

confidence: 99%

Genetic Algorithm Retrieval of Real Refractive Index from Aerosol Distributions that are not Lognormal

Barkey¹,

Kim²,

Paulson³

2010

Aerosol Science and Technology

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Size distributions of real-world aerosols typically deviate substantially from log-normal or other simple mathematical descriptions. The effect of assuming a lognormal shape for distributions that are not well described by this function on the genetic algorithm (GA) retrieval of the real refractive index (m r ) from scattering properties is investigated. Tests using several laboratory-generated ammonium sulfate aerosols with relatively broad bimodal distributions and with synthetic distributions generated by combining two log-normal distributions are examined. Scattering of the ammonium sulfate aerosols was measured with a dual polarization polar nephelometer. Analysis of the GA retrieval with the assumption that the distribution is lognormal for both the ammonium sulfate aerosol and synthetic distorted distributions show that the retrieved m r is within 0.015 of the expected value in all cases tested. The retrieved values for both the mean and the standard deviation of the aerosol size distribution become more inaccurate as the level of distortion increases. In our experiments, the GA determined mean aerosol diameter is always larger than the measured mean because in all of the distorted distributions there are significantly more large particles than the lognormal assumption. The intensity of particle scattering is generally a function of the square of the particle diameter hence as the distortion increases, the larger particles contribute more to the overall scattering on which the GA retrieval is based. We show that assuming a distribution is lognormal could potentially introduce errors in calculating radiative forcing by at least 12%. The total scattering coefficient measured by integrating nephelometers can be off by a factor of 2 for distortion levels similar to those seen in some of our experiments.

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Genetic Algorithm Approach to Particle Identification by Light Scattering

Cited by 20 publications

References 17 publications

Real refractive indices of α‐ and β‐pinene and toluene secondary organic aerosols generated from ozonolysis and photo‐oxidation

Real refractive indices of α‐ and β‐pinene and toluene secondary organic aerosols generated from ozonolysis and photo‐oxidation

Genetic Algorithm Inversion of Dual Polarization Polar Nephelometer Data to Determine Aerosol Refractive Index

Genetic Algorithm Retrieval of Real Refractive Index from Aerosol Distributions that are not Lognormal

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