Aerosol and Cloud Analysis System Sensors
- Cloud Condensation Nuclei Counter
- Scanning Electrical Mobility Spectrometer
- Differential Mobility Analyzer
- Single Particle Soot Photometer – Extended Range
- Wideband Integrated Bio-aerosol Spectrometer
- Aerosol Chemical Speciation Monitor
- Continuous Light Absorption Photometer
Cloud Condensation Nuclei Counter
Sensor: Cloud Condensation Nuclei Counter
Company: Droplet Measurement and Technologies
The CCN counter operates on the principle that diffusion of heat in air is slower than diffusion of water vapor (Roberts and Nenes, 2005). Inside the column, a thermodynamically unstable, supersaturated water vapor condition is created as follows. Water vapor diffuses from the warm, wet column walls toward the centerline at a faster rate than the heat. Figure (left) shows point C along the centerline where the diffusing heat originated higher on the column (red-line, point A) than the diffusing mass (blue line, point B). Assuming the water vapor is saturated at the column wall at all points and the temperature is greater at point B than at point A, the water vapor partial pressure is also greater at point B than at point A. The actual partial pressure of water vapor at point C is equal to the partial pressure of water vapor at point B. The temperature at point C is lower than at point B, however, which means that there is more water vapor (corresponding to the saturation vapor pressure at point B) than thermodynamically allowed.
The CCN measures aerosol particles called cloud condensation nuclei that can form into cloud droplets. The instrument operates by supersaturating sample air to the point where the CCN become detectable particles, which are then sized using an optical particle counter and distributed into 20 bins.
Scanning Electrical Mobility Spectrometer
Sensor: Scanning Electrical Mobility Spectrometer
Company: Brechtel Manufacturing Incorporated
The Scanning Electrical Mobility system (SEMS)’s Differential Mobility Analyzer (DMA) is optimized to size particles over the 10 to 1000 nm or 20 to 2000 nm diameter range for DMA sheath air flow rates between 2.5 and 10 lpm. The DMA selects particles based on the principle of electrical mobility. The size selected monodisperse particles than detected by a Mixing-based Condensation Particle Counter (MCPC) based on the principle of scattering.
SEMS is a scanning mobility spectrometer providing rapid aerosol size distribution measurements from 10 nm to 1.4 µm.
Figure: Sampling schematic of SEMS
Figure: Plot representing the Ambient size distribution measurements with 60 size bins for total scan times between 6 and 60 seconds.
Differential Mobility Analyzer
Sensor: Differential Mobility Analyzer
Model: NO. 3081
Differential Mobility Analyzer (DMA) is optimized to size particles over the 10 to 1000 nm or 20 to 2000 nm diameter range for DMA sheath air flow rates between 2.5 and 10 lpm. The DMA selects particles based on the principle of electrical mobility.
The DMA consists of two electrodes and a flow path in which particles move. When a voltage is applied charged particles are diverted from the straight path in the resulting electrical field and classified based on their electrical mobility. When the voltage is constant the DMA generates monodisperse aerosols from a polydisperse particle source. DMA will alternatively be associated with CCN counter to quantify the hygroscopic characteristics/cloud condensation nuclei activations of size classified aerosols as a function of their supersaturations.
CPD3 is name of the NOAA/ESRL/GMD/Aerosols data processing software. It provides data handling from the acquisition and instrument control level all the way through final export to data archives.
The reason for having CPD3 on the ACAS board was to access the data from the CLAP instrument and the Vaisala meteorological sensors.
Single Particle Soot Photometer – Extended Range
Sensor: Single Particle Soot Photometer – Extended Range
Company: Droplet Measurement Technologies, LLC
Delivers accurate, real-time, size-resolved single particle measurements of black carbon mass and size with direct output suitable for monitoring applications.
SP2-XR uses the laser-induced incandescence principle to accurately quantify the soot fractions in ambient aerosol for long-term monitoring applications. It uses one scattering and one incandescence detector to count the total and soot particles. It utilizes the high optical power intracavity Nd:YAG laser. Light-absorbing particles, mainly black or elemental carbon, absorb energy and are heated to the point of incandescence. The energy emitted in this incandescence is measured, and a quantitative determination of the black carbon mass of the particle is made. This mass measurement is independent of the particle mixing state, and hence the SP2-XR is a reliable measure of the black carbon mass concentration. Since the SP2-XR detects single particles, it also measures the black carbon particle concentration.
Single Particle Soot Photometer-Extended Range (SP2-XR) directly measures refractory black carbon (rBC) in individual particles.
Wideband Integrated Bio-aerosol Spectrometer
Sensor: Wideband Integrated Bio-aerosol Spectrometer
Company: Droplet Measurement and Technologies
The Wideband Integrated Bioaerosol Sensor-New Electronics Option (WIBS-NEO) is designed to provide highly sensitive measurements of bioaerosols. The instrument uses two UV filtered flashlamp sources to excite fluorescence in individual particles. Detection wavebands have been selected to optimize detection of common bioaerosol components such as tryptophan and nicotinamide adenine di-nucleotide (NADH).
The single-particle fluorescence sensor, WIBS-NEO, employs a central optical chamber around which are arranged the following components:
Continuous Light Absorption Photometer
Sensor: Continuous Light Absorption Photometer
The Continuous Light Absorption Photometer (CLAP) measures the aerosol absorption of radiation at three visible wavelengths; 461, 522 and 653 nanometers (nm) based on the continuous measurements of light transmitted through a filter while the aerosols are being deposited on the filter. Data from this measurement is used in radiative forcing calculations, atmospheric heating rates, and as a prediction of the amount of equivalent black carbon in atmospheric aerosol and in models of aerosol semi-direct forcing. Aerosol absorption measurements are essential to modeling the energy balance of the atmosphere.
Continuous Light Absorption Photometer (CLAP) operates at three visible wavelengths (blue, green red), to allow calculation of aerosol absorption coefficients.
The CLAP provides measurement of the light absorption of particles deposited on a filter. It utilizes solenoid valves to cycle through 8 sample filter spots and 2 reference filter spots, enabling the instrument to run at ideal conditions (filter transmittance greater than 0.7). The CLAP uses 47-mm diameter, glass-fiber filters (Pallflex type E70-2075W). These filters are made of two fibrous layers, borosilicate glass fibers overlaying a cellulose fiber backing material (for strength and stability). The cellulose fiber layer is thought to take up water under conditions of high humidity, which is one reason that CLAP has an internal heater to lower the sample relative humidity inside the instrument. The CLAP is typically installed so that it draws its sample air through a modified of ACAS setup. The CLAP vacuum line is connected to a vacuum diaphragm pump.
Tunable Diode Laser Hygrometer
Sensor: Tunable Diode Laser Hygrometer
Company: MayComm Instruments, LLC
Model: Custom Designed Research Instrument
The CMDL laser hygrometer is designed to provide measurements of water vapor mixing ratio (converted to absolute humidity for output) within a heated sample cell resident to the control electronics 1U enclosure. The optical absorption path length is 2.54 cm. A fiber-coupled distributed feedback diode laser continuously scans the H2O spectral line at 7299.4 cm-1 (1370 nm) to provide a second harmonic (2f) spectrum to the control electronics. Four individual spectra are averaged (in approximately one second), then analyzed by the microcontroller software to produce the H2O concentration as absolute humidity in units of g/m3. Pressure and temperature inside the sample cell, required for real-time data processing, are measured using sensors resident to the sample cell. The sample cell is thermostatted at approximately +45 C to avoid condensation of water at the relatively high H2O concentrations that may be encountered.
Water Vapor Mixing Ratio
Constant dew point generation data (chilled mirror vs. TDL as function of pressure) at lower H2O values in the linear range.
Back-Scatter Cloud Probe
Sensor: Back-Scatter Cloud Probe
Company: Droplet Measurement Technology
Sensor: Vaisala PWD
Vaisala PWD22 sensors use the proven forward scatter measurement principle to measure meteorological optical range (MOR). The visibility sensor is well protected against contamination: the optical components point downwards and hoods protect the lenses against precipitation, spray, and dust. This weather-proof design of Vaisala PWD22 sensors provides accurate measurement results and reduces the need for maintenance. The optional hood heaters are recommended for wintry conditions to prevent ice and snow accumulation.
Vaisala PWD present weather detectors and visibility sensors provide the measurement of prevailing visibility. The measurement principles of Vaisala PWD22 enable identify the precipitation type by accurately estimating the water content of precipitation with a capacitive device (Vaisala RAINCAP® sensor element) and combining this information with optical forward scatter and temperature measurements.
Sensor: Vaisala WMT
The wind sensor has an array of three equally spaced ultrasonic transducers on a horizontal plane. Wind speed (WS) and wind direction (WD) are determined by measuring the time it takes the ultrasound to travel from each transducer to the other two. The wind sensor measures the transit time (in both directions) along the three paths established by the array of transducers. This transit time depends on wind speed along the ultrasonic path. For zero wind speed, both the forward and reverse transit times are the same. With wind along the sound path, the upwind direction transit time increases and the downwind transit time decreases.
WMT700 uses the Vaisala WINDCAP ® ultrasonic sensor technology in wind measurement. The sensor has an onboard microcontroller that captures and processes data and communicates over serial interfaces.
Sensor: Vaisala WXT
WXT530 Series has a unique Vaisala solid state sensor technology. To measure wind, Vaisala WINDCAP® ultrasonic wind sensors are applied to determine horizontal wind speed and direction. Barometric pressure, temperature, and humidity measurements are combined in the PTU module using capacitive measurement for each parameter. This module is easy to change without any contact with the sensors. The precipitation measurement is based on the unique acoustic Vaisala RAINCAP® Sensor without flooding, clogging, wetting, and evaporation losses.
The WXT530 is a all-in-one weather instruments. It provides six of the most important weather parameters: air pressure, temperature, humidity, rainfall, wind speed and wind direction.
GCVI Visibility Sensor
Sensor: GCVI Visibility Sensor
Company: Belfort Instrument
The Belfort Model 6500 is a Forward Scatter Visibility Sensor associated with the ground-based counterflow virtual impactor (GCVI) system. The sensor is an indicator (low visibility< 300m) for the counterflow virtual impactor (CVI) inlet to actuate in the presence of clouds or fog. This sensor’s transmitter emits an infrared 890nm wavelength light beam from a 330 mw LED into the sample volume. The light source is modulated to provide excellent rejection of background noise and variations in background light intensity. The receiver will measure the amount of IR light that is forward scattered into the receiver by the particles and aerosols within the sample volume. The Extinction Coefficient is calculated from the amount of detected IR light at the receiver. The Visibility is then calculated from the Extinction Coefficient using the formula “3/Extco value” = visibility in kilometers. This value is then converted to the desired distance measurement.
GCVI Temperature/Humidity Transmitter
Sensor: GCVI Temperature/Humidity Transmitter
Company: DWYER INSTRUMENTS, INC.
RH/T sensor is associated with the ground-based counterflow virtual impactor (GCVI) system. The sensor is an indicator (RH>95%) for the counterflow virtual impactor (CVI) inlet to actuate in the presence of clouds or fog.
GCVI Rain/Snow Sensor Controller
Sensor: GCVI Rain/Snow Sensor Controller
Company: Automated Systems Engineering, INC
The Rain/ Snow sensor is associated with the ground-based counterflow virtual impactor (GCVI) system. The sensor instructs the counterflow virtual impactor (CVI) inlet not to actuate when there is rain (precipitation event).
The Aerosol and Cloud Analysis System (ACAS) is a complex instrument that implements multiple sensors, each of which produce multiple pieces of information that need to be manipulated and stored for data analysis and quality checks and assurance (QC/QA). Data Analysis, Presentation and Training Software (ADAPTS) was developed to serve these functions of data manipulation and storage. The principal objectives of ADAPTS are to:
- Monitor the data streams being produced by each of the ACAS sensors;
- Extract these data and store in a back-up media;
- Conduct preliminary QC/QA and send alerts to the system administrator if potential issues are detected;
ADAPTS is a program that will do the acquisition, store, and display in real-time the data being produced by the instruments of ACAS. It will be useful for analyzing and visualizing the information and data from the ACAS System. The program is implemented in python programming language on its 2.7 version. The ADAPTS graphical user interface (GUI) will require cero programming skills. It will consist of various modules that will dedicate to real the data files, process that data and generate secondary parameters to later display. ADAPTS will count with a dashboard consisting of different build-in views giving access to the features.
Here are the sensors attached to the instrument.