Submicron aerosol number size distribution collected from MPSS at Barrow, Alaska during STUARD

Authors: Saha, S.; Dedrick, J.L.; Russell, L.M.; Leaitch, R.W.

Contact: Sourita Saha. sosaha@ucsd.edu, Lynn Russell. lmrussell@ucsd.edu Scripps Institution of Oceanography, University of California San Diego, La Jolla, CA 92037. 

Cite data: (will add when doi comes)

Data Processing: The particle number size distribution of the atmospheric aerosol is an essential parameter required in calculations of the effects of aerosols on climate, human health, and ecosystems (A. Wiedensohler et al. 2012). This work reports on the clean (or background) submicron aerosol number size distribution during the STUARD campaign at Utqiagvik,  Alaska. 

The DMA (Differential Mobility Analyser) measures submicron aerosol particle sizes from 10-800 nm with an uncertainty of ~10%. The instrument is operated with Mobility Particle Size Spectrometer (MPSS) software for a medium-length Vienna-design DMA operated at 1:5 lpm flow ratio upstream  of a condensation particle counter (TSI 3010 CPC). The instrument records particle number concentration as a function of electrical mobility by varying the DMA voltage. This is inverted to get the number size distribution using a standard inversion routine provided by TROPOS. Particle losses in the inlet, DMA, and associated tubing are corrected for in the inversion routine. Information about the lengths and flow rates used in the loss correction are described below.  

From head down to splitter 	1.82m 	160lpm
Splitter to horizontal stainless steel 	2.02m	30lpm
Black tube from MPSS pick off to capillary 	0.86m	1lpm
Inside DMA (Vienna medium)	4.6m	1lpm
MPSS system 	2.45m	1lpm

As a next step, the inverted data (.in2) have been removed when flags for the following parameters were 1. The flags are turned on 1 for the following reasons:
•Low Vacuum: flow is too low because the dP across the critical orifice is not high enough.  this is equivalent to the flow light on the instrument being off because the proper flow conditions are not achieved.
•CPC High: if CN>4000 per cc.
•CPC Spike: If particle concentration measurement exceeds the last 30-minute average by a factor of 2.5 or more.
•Mentor: fix/maintain some issues with the instrument.
•Wind Speed: Low wind speed <0.5 m/s.
•Wind Direction: wind coming from out of sector (130-360 degrees).
•Instrument Not Ready.

The DMA measured aerosols varying in diameter from 10  to 800nm. Each measurement time is about 5 minutes. After the contamination and instrument flags have been applied to size distribution data, one-hour averaged month-wise data have been stored in a tabular form for further analysis. For processing the flag files, all flags were combined into one flag. There are month-wise flags.  Each month contains an Excel file (column 1 is the day of the month, column 2 is the time (hour+minute/60), column 3 is the combined flag). If the flag value is 1, it means the data corresponding to that time should be discarded. A mask was created which was then applied to the DMA number concentration to obtain only the times when the measured particles are considered representative of background conditions at Utqiagvik. The processed data contains hourly averaged size distribution data for each month from June 2022 to December 2022.
SOFTWARE IMPLEMENTATION: The raw electron mobility data from SMPS were inverted to number size distribution using the TROPOS inversion program (A. Wiedensohler et al. 2012). All the codes to generate the monthly background number size distribution were written to run on MATLAB R2023a. The flag files were processed in Microsoft Excel. 
 
Information about csv file: Each BRW_Processed_XXX_2022.csv file contains processed size distribution data for the entire month (XXX stands for each month). First row is diameter ranges of aerosols in nm measured by the instrument.
First column is day of month.
Second column is hour of the day. 
Third column to the end has information of size distribution (dN/dlogDp) corresponding to the hour of the day.