24
microAeth
®
MA Series MA200, MA300, MA350
Operating Manual
microAeth
®
MA Series MA200, MA300, MA350
Operating Manual
25
AethLabs
AethLabs
4. Measurements
4.1. Particles
The microAeth MA Series instruments make real-time five wavelength optical analyses by measuring the
rate of decrease in transmitted light through the sample filter, due to continuous particle deposition on the
filter. Measurement at 880 nm is interpreted as the concentration of Black Carbon (‘BC’). Measurement at
375 nm is interpreted as Ultraviolet Particulate Matter (‘UVPM’) indicative of woodsmoke, tobacco, and or
biomass burning. Measurements at 625 nm, 528 nm, and 470 nm wavelengths provide additional information
about the aerosol, and allow for the calculation of the angstrom exponent which can be used for source
apportionment and other atmospheric investigations.
4.1.1. DualSpot
®
Loading Compensation (beta)
The microAeth MA Series instruments include hardware and firmware that implement the patented
DualSpot® Loading Compensation method. This method simultaneously collects aerosol samples on two
analysis spots in parallel and at different face velocities while measuring the rate of change in absorption
of transmitted light due to the particles loading on the filter. The use of this method is an optional user
selectable feature.
A flow rate of 100 or 150 ml/min is highly recommended when using DualSpot
®
loading compensation. Although DualSpot mode can be used in many sampling scenerios, for best results
it should be used in stationary applications.
4.2. Temperature
A temperature measurement of the sample air stream is made every Timebase. The sensor value for this
measurement is very close to both the filter sampling locations and the internal mass flowmeters. The
datastream from this sensor is representative of the internal temperature of the sample air and while it may
track changes in external air temperature, it may have a temperature offset compared with actual external
ambient air temperature due to internal heating or cooling of the instrument. This sensor value is always
recorded. In the data output, this value is recorded in the column labeled “Sample temp (C).” The accuracy of
the temperature measurement is typically ± 0.2 °C.
A temperature measurement of the internal chassis of the instrument is made every Timebase. This sensor
value is always recorded. In the data output, this value is recorded in the column labeled “Internal temp
(C).” The accuracy of the temperature measurement is typically ± 1 °C at 25 °C and typically ± 3 °C over the
temperature measurement range of -40 to +85 °C.
4.3. Relative Humidity and Dewpoint
A relative humidity measurement of the sample air stream is made every Timebase. This sensor is coupled to
measurement sample spot sense2. In SingleSpot™ mode there is no active flow through the humidity sensor,
while in DualSpot® mode there is active flow through the humidity sensor. Therefore the measurement will be
more accurate and more responsive in DualSpot® mode. This sensor value is always recorded. In the data
output, this value is recorded in the column labeled “Sample RH (%).” The accuracy of the relative humidity
measurement is typically ± 1.8 %RH between 10-90 %RH at 25 °C.
A dewpoint calculation is made by the instrument every Timebase. This value is always calculated and
recorded using the temperature and relative humidity senors measurements. In the data output, this value is
recorded in the column labeled “Sample dewpoint (C).”
4.4. Altimeter/Barometer
A pressure measurement of the internal chassis of the instrument is made every Timebase. This sensor is
always recorded. In the data output, this value is recorded in the column labeled “Internal pressure (Pa)” The
accuracy of the absolute pressure measurement is typically ± 0.4 kPa at test conditions of 50 to 110 kPa over
−10 °C to 70 °C.
4.5. Accelerometer
A 3-axis acceleration measurement of the internal chassis of the instrument is made every Timebase. This
sensor is always recorded. In the data output, this value is recorded in the columns labeled “Accel X,” “Accel
Y,” and “Accel Z.”
The microAeth has access to the Global Positioning System with a built-in antenna. The GPS is used for
precise, automatic time synchronization and for optional location tracking.
4.7. Flow
Two separate mass flowmeters each make flow measurements of the sample air stream and are recorded
every Timebase. These sensor measurements are always recorded and represent the average flow through
the timebase period (not instantaneous). In the data output, these values are recorded in the column labeled
“Flow total (mL/min)” and “Flow1 (mL/min).” The accuracy of the flow measurements is typically ± 5% FS 0-1
L/min (25 °C characteristic). The repeatability of the flow measurements is typically ±0.4% FS 0-1 L/min.
When the instrument has DualSpot loading compensation enabled, a flow calculation is made by the
instrument every Timebase. This value is always calculated and recorded. In the data output, this value is
recorded in the column labeled “Flow2 (mL/min).”
