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Nitrogen oxides in the free troposphere: implications for tropospheric oxidants and the interpretation of satellite NO2 measurements

Secondary organic aerosols from anthropogenic volatile organic compounds contribute substantially to air pollution mortality

Aerosol pH indicator and organosulfate detectability from aerosol mass spectrometry measurements

Schueneman, M., et al. (2021), Aerosol pH indicator and organosulfate detectability from aerosol mass spectrometry measurements, Atmos. Meas. Tech., 14, 2237-2260, doi:10.5194/amt-14-2237-2021.

Future changes in isoprene-epoxydiol-derived secondary organic aerosol (IEPOX SOA) under the Shared Socioeconomic Pathways: the importance of physicochemical dependency

Fast Cloud Droplet Probe

SPEC has developed a Fast Cloud Droplet Probe (FCDP) with state-of-the-art electro-optics and electronics that utilizes forward scattering to determine cloud droplet distributions and concentrations in the range of 1.5 to 50 microns.  Though designed for cloud droplet measurements, the probe has also shown reliable measurements in ice clouds.  The new electronics include a temperature controlled fiber-coupled laser, FSSP-300 optics with pinhole limiting depth of field (Lance et al. 2010), a field programmable gate array (FPGA), 40 MHz analog-to-digital-converter (ADC) sampling, custom amplifiers, a very small and low power Linux based 400 MHz processor and a 16-Gigabyte flash drive that stores data at the probe.

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Proton-Transfer-Reaction Mass Spectrometer

PTR-MS is a chemical ionization mass spectrometry technique that allows for fast measurements of organic trace gases. In combination with the CHARON inlet, it measures the organic composition of submicrometer aerosol particles.

 

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Langley Wideband Integrated Bioaerosol Sensor

Wideband Integrated Bioaerosol Sensor (WIBS-4A) - Droplet Measurement Technologies.  Dectection of Fluorescent Biological Aerosol Particle (FBAP) number concentrations.  Single particle analysis using dual wavelength (280nm and 370nm by xenon lamps) excitation on two parallel broadband visible-wavelength detectors (310-400nm and 420-650nm). Particles are classified by a combination of fluorescence excitation and emission characteristics, as well as their optical size measured by forward-scattering using a 635nm continuous-wave diode laser.    

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Continuous Flow Streamwise Thermal Gradient CCN Counter

Developed by Droplet Measurement Technologies, the CFSTGC is based on a concept by Roberts and Nenes [2005]. The instrument counts the fraction of aerosol particles that become droplets when exposed to a given water vapor supersaturation (RH > 100%).

As with all CCN counters, a temperature gradient is applied to produce a supersaturation of water vapor. However, the mechanism for generating supersaturation is not the same for all CCN counters. For example, for continuous flow parallel plate diffusion chambers, the temperature gradient is perpendicular to the flow, and supersaturation is a result of the nonlinear dependence of vapor pressure upon temperature. The same mechanism applies for static diffusion cloud chambers, where there is no flow at all.

However, as the name implies, for the Continuous Flow Streamwise Thermal Gradient CCN Counter, the temperature gradient is in the streamwise direction (maintained by thermoelectric coolers). In this case, supersaturation results as a consequence of the greater rate of mass transfer over heat transfer.

With laminar flow, heat and water vapor are transferred to the centerline of the column from the walls only by diffusion.

Since molecular diffusivity is greater than thermal diffusivity, the distance downstream that a water molecule travels before reaching the centerline is less than the distance the heat travels downstream before reaching the centerline. If you pick a point at the centerline, the heat originated from a greater distance upstream than the water vapor.

There are four facts that are necessary to explain how supersaturation is generated within the CFSTGC:

1) Assuming that the inner surface of the column is saturated with water vapor at all points, since 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.

2) The actual partial pressure of water vapor at point C is equal to the partial pressure of water vapor at point B.

3) However, since the temperature at point C is the same as at point A, the equilibrium water vapor pressure at point C is equal to the water vapor partial pressure at point A.

4) The saturation ratio is the ratio between the actual partial pressure of water vapor and the equilibrium vapor pressure. This is equivalent to the partial pressure at point B divided by the partial pressure at point A, which is always greater than one. Thus supersaturation is generated through a dynamic equilibrium.

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Aircraft: 
Balloon, P-3 Orion - WFF, C-130H - WFF, DC-8 - AFRC, HU-25 Falcon - LaRC
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