AMS Readme File GoAmazon (IOP 1) Campaign 2/17 – 3/25/2013 John Shilling, PNNL Revision 2, 3/13/2015 PI contact information: John Shilling Pacific Northwest National Laboratory, Atmospheric Sciences and Global Change Division 902 Battelle Blvd MSIN K4-28 Richland, WA 99352 Ph: 509-375-6874 e-mail: John.shilling@pnnl.gov G-1 AMS data downloaded before March 13th 2015 are Revision 1. Current version of the G-1 AMS data is Revision 2. Revision 2 data file names have _R2 appended onto them. Please contact the instrument PI for any questions regarding this data. Please adhere to the ARM data policy when using this data. Note that suspected "bad" data and data when the instrument is zeroed may be retained in the file and flagged instead of deleted. AMS data was collected on an Aerodyne high-resolution time of flight mass spectrometer during the GoAmazon field campaign in the Manaus, Brazil region. The instrument was flown on the G1 research aircraft from February 18th to March 25th, 2014. The AMS sampled behind a nafion diffusion dyer, which reduced the RH of the airstream to 30-40%. A pressure controlled inlet was used to maintain a constant pressure upstream of the AMS aerodynamic lens. The pressure controlled inlet closely followed the design in Bahreini et al., Aerosol Sci. Technol., 42, 465-471, 10.1080/02786820802178514, 2008. The inlet pressure was set to approximately 620 mbar during the campaign. Due to the inlet pressure setting, the AMS was not able to maintain a constant sample flow above altitudes of ~10,000 ft. Data at altitudes > 10,000ft are still included in the files, but flagged. In general, the data at these altitudes will be less accurate than data at lower altitudes, though I have attempted to correct the data for the reduced flow. For questions regarding the use of the high-altitude data, contact the PI. Files are in tab delimited files. The single-line header information gives the date and time, species name, approximate error for the unit mass resolution (UMR) species, and a flag wave. Date and time are local time (Manaus, Brazil). The flag column indicates the instrument status, data quality, and sampling inlet. A value of 0 indicates good data, 1 indicates zero periods, 2 indicates known bad data that should not be used in analysis, 3 indicates data when the sample flow was somewhat unstable and that should be OK, but will have somewhat higher uncertainty than typical, and 4 indicates data taken when the AMS sample flow began to decrease (above 10k ft) and should be used with caution. The data interval is 12s. Time stamps represent the end of the averaging period. The instrument was run only in V-MS mode. Therefore, there is no size distribution data. Data files contain the time trace of the unit mass resolution organics (labeled "org"), sulfate ("SO4"), nitrate ("NO3"), ammonium ("NH4"), and chloride ("Chl") in units of micrograms per cubic meter. The approximate error of each measurement is also given in a wave labeled with the species name and "_err". For example, the error on the organic concentration is labeled org_err. Measurements are normalized to laboratory conditions of 23 C and 1 atmosphere pressure. The standard AMS fragment table has been adjusted to account for gas-phase species by diverting the sample flow periodically through a HEPA filter, which removes particles from the airstream. Signal intensity is converted to ug/m^3 according to procedures found in the literature. See for example Jimenez et al, J. Geophys. Res., 108, 8425, 2003 and Allan et al., J Geophys, Res, 108,4090, 2003. Instrument IE and ammonium RIE were calibrated several times throughout the campaign in the field using standard procedures and monodisperse ammonium nitrate particles (CPC method). The UMR ammonium data are noisy because concentrations are low. I strongly recommend using the HR ammonium concentrations which are labeled as HR_NH4. Revision 2, March 13th 2015 The previous version of the G-1 AMS data assumed CE=1 based on analysis of the T3 (Manacaparu) AMS data during IOP1 (wet season). In addition, some reports suggest that CE=1 is appropriate for aerosol in the Amazon region (Chen et al, GRL, 36, L20806, 2009). Evaluation of the AMS concentrations relative to the UHSAS, FIMS, and PCASP instruments onboard the G-1 suggest a CE of 0.5 is more appropriate for the G-1 AMS. Therefore data were revised on March 13, 2015 and CE=0.5 was applied to the G-1 AMS data. In previous field campaigns, the CE of this instrument has been evaluated as CE=0.5. For those who wish to update their data analysis without re-downloading data, all Revision 1 species concentrations and error values can be multiplied by 2. It is currently unclear why there is an apparent differenced in CE’s of the G-1 and T3 AMS instruments. For further questions, please contact John Shilling. (john.shilling@pnnl.gov). Notes on specific flights: 3/10/2014 – AMS data not available this day.