FTIR Organic Functional Group Mass Concentration collected at Barrow, Alaska during STUARD

Authors: Saha, S.; Pelayo, C.; Russell, L.M.

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 we get doi)

ABSTRACT: Beginning in July 2022, automated organic filter measurements were maintained by NOAA ESRL staff using an 8-sample rotating filter holder. Computer-controlled solenoid valves downstream of the filters open and close sequentially so that one filter is sampled at a time. The filter holder exposes 8 different 47 mm diameter Teflon filters to ambient air pulled through a warmed inlet at 30 L min−1. Seven submicron filter samples are collected each for 1 to 5 days depending on the time of year and the aerosol loading. One filter serves as a sampling blank and is exposed to sample air for 10 s (Quinn et al 2002). To avoid contamination from the town of Utqiagvik, sector control was used to collect samples only when wind speed was above 0.5 m s−1 and direction was between 0° and 130° and CN<1000 cc. The filters are then shipped frozen to San Diego and the samples are analysed using a Fourier transform infrared (FTIR) spectrometer in a temperature and humidity-controlled clean room to measure the absorption of organic functional groups and convert them to mass [Maria et al., 2002; Gilardoni et al., 2007] using an automated algorithm [Russell et al., 2009]. The mass concentrations derived from the algorithm are subjected to the following criteria to cross the detection level. Below detection level is decided as the maximum of 2 standard deviation of the functional groups and at least two functional groups have to be present in the sample for it to be considered in the analysis. Further, the standard deviation of acid has been replaced by the standard deviation of carbonyl as it has more prominent peaks.  
SOFTWARE IMPLEMENTATION: The data analysis was done in R Studio.

Information about data file: Raw and Processed Data contains baselines, dpt files, and mass concentration data. 
Baselines contain month-wise baselined pdf and UTQ.bl-rda file which contains the baselined absorption spectra. 
DPT folder contains prescan, postscan dpt files month-wise, and the dpt files for the blanks used for this campaign in 2022. 
FTIR MASS CONC.xlsx contains the data about the mass concentrations of different organic functional groups. 
All the time is recorded in UTC. 

In the summary plot, the xticks represent each day of the year. Some have the same bar for 4 days because the same sample has been used for 4 days, for example, during summer when the aerosol mass concentration is very low. The bars represent the sampling time of each filter. January to April runs on one filter per day, May runs on one filter per two days, June-October runs on one filter per four days and November-December runs on one filter per two days.

The days with carbonyl in July-Aug corresponds to fire events nearby.