Examples of Typical Aethalometer Data

Single Wavelength | Dual Wavelength | Spectrum (Seven) Wavelength

The real-time nature of Aethalometer data provides a wealth of information that allows for interpretation of the data patterns in terms of source strengths, emission patterns, meteorological effects, and all other factors that influence the immediate concentration of particulates in the air.  This information potential greatly exceeds that from measurements integrated over longer timebases, e.g. 30-minute to 8- or 24-hour samples.  The links on this page show graphics from a variety of Aethalometer applications highlighting the value of continuous measurement technology.  We will continue to add to the illustrations linked to this page as more data and interesting results are posted.

Data Examples - Conventional Single-Channel "BC" Aethalometer

Click here for two charts taken from a recent publication (Atmospheric Environment 33, (1999), p. 817, G. A. Allen et al.) comparing Aethalometer data with thermochemical analysis of filter samples and with data collected from a 'Coefficient Of Haze' instrument. The results show excellent agreement, indicating that the Aethalometer output can be directly related to other familiar techniques.

Click here for two charts comparing 24-hour overlays of data taken with an Aethalometer during two summer months in Phoenix, Arizona.  The first chart shows the overlay of many weekdays' data (i.e. Monday - Friday) : high concentrations are seen, with individual peaks probably due to vehicles near the measurement site.  The typical traffic pattern is very clear, and the mid-day minimum is due to lifting of the temperature inversion and increased vertical mixing.  The second chart shows the overlay of data taken on holidays - i.e. Sundays and the July-4th holiday.  On these days, the concentrations are much lower and show very little diurnal variation.  The conclusions available from these charts and their comparisons are immediately obvious.  This illustrates the power and usefulness of real-time data.

Click here for a chart showing 24-hour overlays of data taken with an Aethalometer during a winter month in Denver, Colorado.  The chart shows the clear patterns of source strength (traffic emissions and evening fireplaces), but with a very strong afternoon clearing due to regular downslope winds.  Data such as this allow for immediately obvious interpretation.  This illustrates the power and usefulness of real-time data.

Click here for a chart illustrating data taken while driving on the freeway with an Aethalometer operating on the passenger seat of a car, powered through a small inverter from the cigarette-lighter socket.

Click here for charts illustrating data taken under clean air conditions of strong wind from the ocean, illustrating the dynamic range and sensitivity of the Aethalometer.

Data Examples - Dual-Channel "UV + BC" Aethalometer

Click here for a sequence of charts showing measurements taken with the Dual Wavelength Aethalometer in a heavy-vehicle maintenance garage: i.e. an enclosed environment within which gasoline and diesel engines were run from time to time.  The UVPM channel tracks the BC channel for "pure elemental carbon" particles: however, in some instances, enhancements in the UVPM signal indicate the presence of additional quantities of non-black, UV-absorbing organic compounds attributable to fresh diesel exhaust.  While this measurement is non-quantitative, it clearly signals (in real time) the presence of these aromatic compounds.

Click here for a chart showing measurements taken with the Dual Wavelength Aethalometer in a large enclosed space (an exhibition hall) into which a diesel vehicle was driven.  The UVPM channel tracks the BC channel for "pure elemental carbon" particles: when the hall doors were opened at 8:30 AM, both traces begin to rise.  However, the fresh diesel exhaust appears as an enhancement in the UVPM signal, indicating the presence of additional quantities of non-black, UV-absorbing aromatic organic filterable material.

Click here for charts showing the response of the Dual Wavelength Aethalometer to tobacco smoke. The first two charts from a test chamber compare the UVPM channel response with the results of 'standard' tobacco smoke quantitation methods, namely gravimetric mass and UV-spectrometric absorbance. However, both of these standard methods are laborious and time-consuming, and require the collection of filter samples over fairly long periods of time. The second two charts of real-time Dual Wavelength Aethalometer data show results that would be impossible to obtain by conventional means. The first of these shows a set of first-order decay curves tracking the dissipation of UV signal (i.e. tobacco smoke tracer) in a small unventilated room, from 10 to 180 minutes after cigarette smoking. This allows for calculation of the dispersal and depositional loss of ETS aerosol. The second chart shows a time series of measurements in the same office: smoking was only permitted at certain hours, but fresh vehicle exhaust is also seen.

Data Examples - "Spectrum" or Seven Wavelength Aethalometer

The "Spectrum" Aethalometer acquires data in seven channels at wavelengths ranging from ultraviolet to near-infrared, namely 370, 450, 571, 615, 660, 880 and 950 nm. The algorithm converts the incremental optical signal in each channel to a mass of material using a cross-section assuming spectrally-uniform absorbance, i.e. absorption proportional to photon energy, SIGMA = k / LAMBDA. If the aerosol consisted only of extremely small pure black spheres, the signals in all channels would be interpreted identically as the same mass of material, and the seven data chart traces would be perfectly superimposed. Deviations from this spectral uniformity could be caused by several factors. Examples include: large particle size (more absorption per unit mass in red, less in blue); presence of aromatic organic compounds (onset of enhanced absorbance in blue and ultraviolet channels); colored mineral dust (extra absorption in particular channel); and other effects due to specific details of the aerosol composition. The "Spectrum" Aethalometer is intended for research applications in the fields of atmospheric radiative transfer, aerosol optics, etc. At present we do not know the reasons for deviations from the 1/lambda absorbance law, and we hope that use of the instrument will lead to an enhanced understanding of aerosol optical properties.

Click here for a series of charts showing measurements taken of ambient air under clean conditions in Berkeley, California. On-shore winds from the Pacific Ocean result in concentrations lower than 100 ng/m3 at times, even in an urban area of several millions' population. Most of the time, the seven channel traces are superimposed, indicating that the aerosol absorbance is spectrally "pure", i.e. most likely due to micrographitic elemental carbon. However, there are clearly times when the 'green' channel signal is lower than the other 6 channels. We have no good explanation for this at the present time, that's why research is so interesting.

 


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