NCSU HTDMA data

Data Level b1: QC checks applied to measurements
Data Format: CSV
Description: See "instrument description
Site: Houston, TX; Tracking Aerosol Convection interactions ExpeRiment (HOU)
Location: Houston, TX; AMF1 (main site for TRACER)
Facility Code: M1
Category: Aerosol Properties
Data Type: PI Data
Source Instrument/Data: Humidified Tandem Differential Mobility Analyzer; 2 Differential Mobility Analyzers (DMA1 and DMA2).
Start Date: 2022-06-01
End Date: 2022-09-26
Contact PI: Markus Petters (mdpetter@ncsu.edu)
Funding Source: DOE ASR award US Department of Energy, Office of Science, Biological and Environment Research (grant no. DE-SC 0021074)

Instrument description

The NCSU HTDMA was operated at a sheath-to-sample flow ratio of 5:1 L min−1. The HTDMA was configured to measure hygroscopic growth factors of dry particles with mobility diameters of D = 15, 20, 30, 40, and 50 nm at RH ~ 70%. A complete cycle for all diameters took ~30 minutes. A sample line brought aerosol inside the trailer at 2.5 L min-1, where it was distributed between NCSU RDMA (1.5 L min-1) and NCSU HTDMA (1 L min-1) lines. The sample line was dried with three silica-gel driers in series, and then neutralized with X-ray neutralizer. The sample line entered DMA1 (operated as an electrostatic classifier). Monodisperse particles with certain fractions were humidified with temperature controlled Nafion membrane immersed in water before entering DMA2 (operated in scanning mobility particle sizer). Please contact mdpetter@ncsu.edu for further information.

The purpose of the dataset it measure the growth of sub-50 nm due to water uptake. This allows the inferences of aerosol mixing state as well as   

Quality assurance and quality control

 The 10 Hz raw data from the NCSU HTDMA were acquired using a custom data acquisition system that logged time at UTC. Data during general instrument maintenance, data outages during storms, and suspected instrument malfunction, and during HTDMA calibrations are removed. Calibrated RH values are given below. Examples of general instrument maintenance are HTDMA calibrations, and renewing silica gels in the dryers. A dilute ammonium sulfate particles were used to calibrate the HTDMA. Example of instrument malfunction are power outages and water build up in the dryers that needs to be replaced.

Calibration

The calibration of the Rotronic RH sensor of the humidified tandem differential mobility analyzer (NCSU HTDMA) was calibrated with diluted ammonium sulfate particles.    Atomized ammonium sulfate particles (1 L min-1) were routed into silica-gel driers in series and then neutralized with an X-ray neutralizer before entering DMA1 (operated as an electrostatic classifier). Monodisperse particles with certain fractions were humidified with a temperature-controlled Nafion membrane immersed in water before entering DMA2 (operated in scanning mobility particle sizer). The calibration took at least 20 minutes. The observed size of the humidified ammonium sulfate particles by DMA2 was used with Extended Aerosol Inorganic Model (E-AIM) (Clegg and Seinfeld, 2006; Wexler and Clegg, 2022; Clegg, 2007) at measured RH to infer the calibrated RH of the instrument (Suda and Petters, 2013). The model retrieves the calculated RH as a function of growth factor (gf) at specific dry diameters of 15, 20, 30, 40, and 50 nm particles. Growth factors were measured by the ratio of the size distributions retrieved from DMA1 and DMA2.