DOI: 10.5066/f7j965m3
title: Bromide wet deposition concentrations in the contiguous United States, 2001-2016

description: Summary: The National Atmospheric Deposition Program (NADP) has monitored the concentrations of solutes in precipitation in the U.S. since 1978 for assessment of air pollution controls and the effects of air pollution deposited to the landscape. In 2009, the NADP added bromide (Br-) to its routine analytical schedules for its National Trends Network (NTN) and Atmospheric Integrated Research Monitoring Network (AIRMoN). This dataset includes the NTN and AIRMoN Br- concentration data collected from 2009-2016 augmented with data from archived NTN samples collected 2001-2009. Since 2009, the NTN has included approximately 250 sites in the contiguous U.S., which is the focus of this study. Data for sites in Alaska, Puerto Rico, U.S. Virgin Islands, and Argentina are not included.   Weekly composite NADP/NTN "wet-only deposition" samples were collected with Aerochem Metrics model 301 and N-CON model ADS 00-120 collectors. The NTN samples were removed from the collectors every Tuesday morning and decanted from plastic collector buckets into 1-liter volume Nalgene bottles. The AIRMoN samples were collected in the same way, but the buckets were lined with clean-room grade plastic bags beginning in October 2014. Important differences with AIRMoN sampling include refrigeration after collection, daily sample removal when precipitation occurs, and analysis without prior filtration. NTN samples are filtered (0.45-micrometer polyethersulfone). All NADP NTN and AIRMoN samples are shipped to the NADP Central Analytical Laboratory (CAL) in Champaign, Illinois, where they are analyzed for: calcium (Ca+2), magnesium (Mg+2), sodium (Na+), potassium (K+), ammonium (NH4+), chloride (Cl-), Br-, nitrate (NO3-), sulfate (SO4-2), orthophosphate (PO4-3), pH, and specific conductance. Given sufficient volume, split samples are stored in a refrigerated archive for at least 5 years for additional uses and analyses by request. Collector buckets and sample bottles are reused after being washed in laboratory washers using only deionized water. Sampling supplies are tested for cleanliness with respect to NADP analytes and bagged in cleanroom-grade plastic bags prior to field deployment (Gartman, 2017).   Data for this study are available from the NADP at http://nadp.sws.uiuc.edu/data/NTN/ and http://nadp.sws.uiuc.edu/data/MDN/, but Br- data have historically only been available by contacting the NADP Database Manager and are now provided within this data release. Unrounded laboratory instrument values for sample analyte concentrations were obtained directly from the CAL database on August 10, 2016 because Br- results were not available from the NADP web site (http://nadp.isws.illinois.edu/NTN/). Concentrations must be multiplied by analytical dilution factors (provided), and then values below the annually reported detection limits may be qualified as censored.   Data for event-based wet deposition samples collected at 7 AIRMoN sites were also obtained for the period July 2009-June 2016. The AIRMoN data were analyzed separately from the NTN data because AIRMoN samples are collected on a daily event basis whereas NTN samples are collected as weekly composite samples. NADP data are quality assured by internal and external programs which are documented on the NADP web site: http://nadp.sws.uiuc.edu/QA/ and http://nadp.sws.uiuc.edu/lib/. Analytical procedures for NTN and AIRMoN samples are available on the CAL web site: http://nadp.sws.uiuc.edu/cal/analytical_capabilities.html. Data obtained for this study were evaluated for completeness and consistency.   The USGS operates an external, independent quality assurance project to assure data quality (https://bqs.usgs.gov/PCQA/). Sample results with missing Br- values were not included. Samples with Br- values of  "0" indicate no Br- was quantified by the analytical method, and these values were considered to be valid measurements below the analytical detection limits of 0.004-0.005 mg/L. In the final data set, zeros were expressed as censored values, and quantified Br- values were censored by the applicable detection limit, which is calculated and reported annually by NADP. To accompany the measurement of weekly wet-deposition concentrations, precipitation depth is continuously recorded by rain gages at all NADP wet-deposition monitoring sites. Precipitation-depth data are monitored and corrected by the NADP Program Office for variability and bias caused by infrequent false positive gage measurements. Every gage and its data are inspected weekly, and gages are independently tested and recalibrated when necessary and at least every 3 years.   Description of files in data release:   AIRMoN_Br_2009-2016.csv:  Event-based data from NADP Atmospheric Integrated Research Monitoring sites, 2009-2016.   Detection_Limits.csv: Analytical detection limits for chemical analyses of precipitation samples at the NADP Central Analytical Laboratory, Champaign, IL.   NTN_Bromide_2001_2016_AL02_MD13.csv: Weekly precipitation sample analysis data obtained from the NADP Central Analytical Laboratory for the period 2001-2016 for National Trends Network sites AL02 through MD13.   NTN_Bromide_2001_2016_MD15_WY99.csv: Weekly precipitation sample analysis data obtained from the NADP Central Analytical Laboratory for the period 2001-2016 for National Trends Network sites MD15 through WY99.   NTN_Data_Fields.csv: Descriptions of each field for National Trends Network data.   AIRMoN_Data_Fields.csv: Descriptions of each field for Atmospheric Integrated Research Monitoring Network data.   References:   Gartman, N., 2017, Quality Assurance Report, National Atmospheric Deposition Program, 2016, NADP Central Analytical Laboratory, Champaign, IL., 65 p, accessed December 6, 2017 at http://nadp.sws.uiuc.edu/lib/qa/cal_qar_2016.pdf.