The Aerosol Quality Characterization System (AQCS) A Different Approach for Identifying Particle Properties

Transcription

1 The Aerosol Quality Characterization System (AQCS) A Different Approach for Identifying Particle Properties Darrel Baumgardner Centro de Ciencias de la Atmosfera Universidad Nacional Autonoma de Mexico Gregory L. Kok Droplet Measurement Technologies A&WMA International Specialty Conference: Leapfrogging Opportunities for Air Quality Improvement May 10-14, 2010 Xi an, Shaanxi Province, China

2 The impact of atmospheric aerosol particles on the environment depends on their concentration, size, shape, optical properties and composition.

3 The impact of atmospheric aerosol particles on the environment depends on their concentration, size, shape, optical properties and composition. Numerous studies have been conducted that relate the volatility, hygroscopicity, y size and optical properties to their chemical composition.

4 The impact of atmospheric aerosol particles on the environment depends on their concentration, size, shape, optical properties and composition. Numerous studies have been conducted that relate the volatility, hygroscopicity and optical properties to their chemical composition. The particle composition and age can be estimated using heating and humidification combined with measurements of size distributions. Many other studies have investigated the relationship between the optical properties of aerosols and their volatility and hygroscopicity.

5 The impact of atmospheric aerosol particles on the environment depends on their concentration, size, shape, optical properties and composition. Numerous studies have been conducted that relate the volatility, hygroscopicity and optical properties to their chemical composition. Volatility measurements can differentiate sea salt from sulfate and identify organic compounds. The particle composition and age can be estimated using heating and humidification combined with measurements of size distributions. ib ti Many other studies have investigated the relationship between the optical properties of aerosols and their volatility and hygroscopicity. A lot of information can be obtained about aerosol composition using a system of sophisticated instruments, as has been demonstrated by a relatively small number of investigators in selected laboratory settings and field sites. What is needed now is to expand the climatological data base with more measurements.

6 The impact of atmospheric aerosol particles on the environment depends on their concentration, size, shape, optical properties and composition. Numerous studies have been conducted that relate the volatility, hygroscopicity and optical properties to their chemical composition. Volatility measurements can differentiate sea salt from sulfate and identify organic compounds. The particle composition and age can be estimated using combinations of hygroscopicity it and volatility. Many other studies have investigated t the relationship between the optical properties of aerosols and their volatility and hygroscopicity. A lot of information can be obtained about aerosol composition with a system of sophisticated instruments, as has been demonstrated by a small number of investigators in selected laboratory settings and field sites. What is needed now is to expand the climatological data base with more measurements. H d thi? M k il bl th hi ti t d How can we do this? Make available the more sophisticated measurement systems for air quality monitoring networks.

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8 The Aerosol Quality Characterization System AQCS Basic Components Aerosol Conditioner Size/Shape Analyzer Particle Optics Analyzer Analyzer/Controller

9 AQCS - Implementation

10 Photoacoustic Technology: No filters, no interference from light scattering and can be calibrated. Aerosols absorb laser light and heat the surrounding air Aerosols absorb laser light and heat the surrounding air (1-2º C) causing pressure wave.

11 Like its larger predecessor (PASS), the PAX is the ONLY instrument that simultaneously measures light absorption.

12 and scattering in order to derive extinction, the parameter needed for visibility and climate change studies.

13 The Aerosol Quality Characterization System

14 Aerosol Particle Spectrometer with Depolarization (APSD) * * Note: A version of the APSD recently measured volcanic ash from a British research aircraft.

15 We derive refractive index (composition) and shape information with measurements of light scattering from two angles 1.6 Aspect Ratio, D = 5 μm Refractive Index, D = 5 μm Refractiv ve Index Aspect Ratio 1.35 Zone of ambiguity Forward to Back Scattering Ratio

16 We derive additional shape information with measurements of light depolarization 5 kscattering Counts Depola arized Bac Psl nm Iron Oxide Silicon Oxide Urban Dust Arizona Dust Backward Scattering Counts

17 Additional particle characteristics are estimated using a neural network that is trained using known relationships among the physical, optical and chemical properties of particles. Scattering Coefficient i Inlet Humidity

18 Particle mass can be derived directly from the scattering and absorption measurements of the PAX, as shown in this example that compares inorganic, organic and total mass measured with an AMS during MILAGRO and extinction derived from a PASS. The red solid line shows a simulation assuming log normal size distributions and a mixture of 50/50 organics and inorganics Simulation 50% Organic 50% Inorganic MILAGRO - AMS Organics MILAGRO - AMS Inorganics MILAGRO - AMS Total Mass Concentra ation (μg m -3 ) Specific Extinction (m 2 g -1 ) Measured = 0.6 +/- 0.4 Modeled = nm PASS Extinction Coefficient (Mm -1 )

19 The AQCS is trained with size resolved chemical measurements from auxiliary instruments such as AMS, ATOFMS, PILS, filter analysis, or even sophisticated chemical transport models like WRF-CHEM. Once trained, the AQCS will operate independently of the auxiliary measurements. This approach will work particularly well, for example, in urban areas such as Beijing, Los Angeles or Mexico City where major field campaigns have been conducted and large data sets of physical, optical and chemical properties are available to do the neural net training.

20 This is an example of particle composition derived from MILAGRO measurements using scattering, absorption and size distributions as the input to a three layer neural net and trained with AMS measurements.

21 Work in Progress A prototype AQCS is currently being evaluated by the University of Manchester. This unit has the APSD, PASS and a CCN. The volatilization unit has not yet been implemented. Commercial versions of the AQCS will be available in mid For more information: darrel.baumgardner@gmail.com