ASTM_D_5015_-_15.pdf

Designation:D501515Standard Test Method forpH of Atmospheric Wet Deposition Samples byElectrometric Determination1This standard is issued under the fixed designation D5015;the number immediately following the designation indicates the year oforiginal adoption or,in the case of revision,the year of last revision.A number in parentheses indicates the year of last reapproval.Asuperscript epsilon()indicates an editorial change since the last revision or reapproval.1.Scope1.1 This test method is applicable to the determination ofpH in atmospheric wet deposition samples by electrometricmeasurement using either a pH half cell with a reference probeor a combination electrode as the sensor.1.2 The values stated in SI units are to be regarded asstandard.No other units of measurement are included in thisstandard.1.3 This standard does not purport to address all of thesafety concerns,if any,associated with its use.It is theresponsibility of the user of this standard to establish appro-priate safety and health practices and determine the applica-bility of regulatory limitations prior to use.1.4 WarningMercury has been designated by many regu-latory agencies as a hazardous material that can cause seriousmedical issues.Mercury,or its vapor,has been demonstrated tobe hazardous to health and corrosive to materials.Cautionshould be taken when handling mercury and mercury contain-ing products.See the applicable product Safety Data Sheet(SDS)for additional information.Users should be aware thatselling mercury or mercury-containing products into your stateor country may be prohibited by law.2.Referenced Documents2.1 ASTM Standards:2D1129 Terminology Relating to WaterD1193 Specification for Reagent WaterD1356 Terminology Relating to Sampling and Analysis ofAtmospheresD2777 Practice for Determination of Precision and Bias ofApplicable Test Methods of Committee D19 on WaterD5012 Guide for Preparation of Materials Used for theCollection and Preservation of Atmospheric Wet Deposi-tionD5111 Guide for Choosing Locations and Sampling Meth-ods to Monitor Atmospheric Deposition at Non-UrbanLocationsE1 Specification for ASTM Liquid-in-Glass ThermometersE2251 Specification for Liquid-in-Glass ASTM Thermom-eters with Low-Hazard Precision LiquidsIEEE/ASTM SI-10 American National Standard for MetricPractice3.Terminology3.1 Definitions:3.1.1 pHthe negative logarithm to the base ten of theconventional hydrogen ion activity.3.1.2 For definitions of other terms used in this test method,refer to Terminologies D1129 and D1356.For an explanationof the metric system including units,symbols,and conversionfactors,see IEEE/ASTM SI-10.4.Summary of Test Method4.1 The pH meter and the associated electrodes are cali-brated with two reference buffer solutions that bracket theanticipated sample pH.The pH of the wet deposition sample isdetermined from this calibration and a quality control standard.The quality control standard is necessary in this application toevaluate the bias due to residual liquid junction potentials andto correct for this bias.4.2 The pH of a solution is related to the EMF(millivolts)of a pH electrode system according to the operational definitionfor a two-point calibration:pHX!5 pHS1!1EX2 ES1ES22 ES1pHS2!2 pHS1!#(1)where:pH(X)=pH of an unknown sample,pH(S1)=pH of a Standard Solution 1,pH(S2)=pH of a Standard Solution 2,EX=EMF(mV)measured in an unknown sample,ES1=EMF(mV)measured in Standard Solution 1,andES2=EMF(mV)measured in Standard Solution 2.1This test method is under the jurisdiction of ASTM Committee D22 on AirQuality and is the direct responsibility of Subcommittee D22.03 on AmbientAtmospheres and Source Emissions.Current edition approved April 1,2015.Published April 2015.Originallyapproved in 1989.Last previous edition approved in 2008 as D5015 02(2008).DOI:10.1520/D5015-15.2For referenced ASTM standards,visit the ASTM website,www.astm.org,orcontact ASTM Customer Service at serviceastm.org.For Annual Book of ASTMStandards volume information,refer to the standards Document Summary page onthe ASTM website.Copyright ASTM International,100 Barr Harbor Drive,PO Box C700,West Conshohocken,PA 19428-2959.United States1 5.Significance and Use5.1 The accurate measurement of pH in atmospheric wetdeposition is an essential and critically important component inthe monitoring of atmospheric wet deposition for trends in theacidity and overall air quality.Atmospheric wet deposition is,in general,a low ionic strength,unbuffered solution.Specialprecautions,as detailed in this test method,are necessary toensure accurate pH measurements(1).3Special emphasis mustbe placed on minimizing the effect of the residual liquidjunction potential bias.5.2 This test method is applicable only to the measurementof pH in atmospheric wet deposition.Its use in other applica-tions may result in inaccuracies.5.3 Fig.1 provides a frequency distribution of precipitationpH values measured in conjunction with a national monitoringprogram within the United States.These dat