NCSU Flux Tower

Data Level b1: QC checks applied to measurements
Data Format: CSV
Description: See "instrument descripotion
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: Sonic Anemometer, 3 Condensation Particle Counters, 1 SP2, 1 POPS
Start Date: 2022-06-01
End Date: 2022-9-26
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 flux tower was located next to the AMF sampling pad. The flux tower consisted of a 10 m telescoping tower. Mounted at the top of the tower was a sonic anemometer (RM Young 8000) and a Krypton Hygrometer. A sample line (¼” conductive tubing) and communication line was laid to a trailer located underneath and slightly adjacent to the tower. The sample line brought aerosol inside the trailer at 4.5 L min-1, where it was distributed between 3 CPCs (TSI 3776c, Dc ~ 2.5 nm, TSI 3771, Dc ~10nm, and TSI 3772, Dc ~40 nm) with different size cuts. Also sampling was a printed particle optical spectrometer (POPS) and a single particle soot photometer (SP2).  Please contact mdpetter@ncsu.edu for further information.

The purpose of this dataset is (1) high time resolution characterization of aerosol properties, (2) determination of fluxes using the eddy-covariance technique. The aerosol data in the file are aligned relative to each other (see alignment tests below and  associated test times in the data file). However, no lag was applied between the sonic anemometer and the aerosol measurements. We estimate that the lag is between 8 and 12 seconds. The precise value will have to be determined through lagged covariance.   

Alignment tests  

The data from the tower were acquired using a custom data acquisition system that logged time at UTC. Due to transport from the top of the tower into the trailer, the three CPCs and the POPS have slightly different arrival times. Alignment tests were performed to pass particles through tubing of approximately similar length than the tubing to the top of the tower. A 3-way valve, one side open to the room and one side capped with a HEPA filter was placed at the end of the tubing. Toggling the valve provides information about the net instrument response time and relative alignment. For each filter toggle, t50 values corresponding to the time where concentration went from 0-50% or 100-50% was calculated and averaged over several filter toggles. The lagging data streams were shifted such that the particle time series are all aligned in the data file. Filter tests were not removed from the data and occurred during the times noted below. For days with no filter test mean t50 values were used to correct for delay. The SP2 sampled on its own clock, which was subject to additional drift compared to the other particle sensors (3 CPCs and 1 POPS). Note that no correction was made to align to the data in time with the sonic anemometer.