WPC  HQey#vЩtYm|^N(wF,0\Ku^x47Aj[&D!e kϙ`&S2cU=l iZF~^y=^s8\:L E? %ɵZ'3m S#ORlY! Tko~fȡ[͓=̎B*U0L %|U. 0hV 0GM 0 C# f= a? BS fp ar f a f a f a  nX 0t0  - U0 U.j/U0U.GU0>U.n h h h h hw4*  `CG TimesX<6X9`(Courier  -'       nXX|n (#(#K(#@EMISSIONMEASUREMENTCENTER@hh!GUIDELINEDOCUMENT(#(#K(# (g2-$ !    X      ^ -)       nXX|n(#(#K(#PreparedbyLoriTusseyLay@@A(# EMCGD037  ` EmissionMeasurementCenter,OAQPS,EPAxx?(#October1988  (#(#K(#(g2-$ !    X      =  -(       nXX|n(#(#K(#EMTICGD037@<<<EMTICGuidelineDocument (#Page  2  ڈ ` (#(#K(#(g2-$ !    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X     nXX|n@  SULFURDIOXIDEINTERFERENCEINMETHODS7AND7A     INTRODUCTION      Athighlevelsofsulfurdioxide(SO2)concentrations,Method7and7A P  havebeenreportedtoyieldlownitrogen(NOx)results.Itwasbelievedthat 8 SO2depletesthehydrogenperoxide(H2O2)intheabsorbingsolution,whichthen  causesincompleteabsorptionoftheNOx.TheconcentrationofH2O2inthe ` absorbingsolutionhasthereforebeenincreased.Forexample,theAmericanSocietyofTestingandMaterialsMethodD1608[TestMethodforOxidesofNitrogeninGaseousCombustionProducts(PhenoldisulfonicAcid)]usesanabsorbingsolutioncontainingH2O2thatisequivalenttofivetimesthe  X  concentrationcurrentlyspecifiedinEPAMethod7.  Alaboratorystudywasconductedto(1)determinewhetherSO2isan 0h  interferentand(2)correcttheproblemifoneexists. TESTINGANDDISCUSSION  @x    TodeterminewhetherSO2interferes,severalsetsofsampleswithvaried   amountsofSO2werecollectedandanalyzedaccordingtoMethod7Ausingthe \ sameabsorbingsolutionasMethod7.TheresultsareshowninTable1.TheNOxresultsindicatethatSO2beginstointerfereatabout2100ppmSO2.    TheconcentrationofH2O2intheabsorbentwasthenincreased.Samples T weretakenwithatleast2000ppmSO2andwithanabsorbingsolutionhavinga  H2O2concentrationfourtimestheoriginalstrength.Theresultsofthis | seriesoftestsarereportedinTable2.Overall,theincreasedH2O2solution ,d showedsomeimprovementcomparedtotheregularMethod7solution;however,theprecisionandaccuracywerestillpoor.AsecondsetofsampleswastakenwiththeincreasedH2O2andanalyzedbybothMethods7and7Atodetermineif <t theincreasedH2O2interferredwiththeionchromatograph(IC).Theresults $  inTable3indicatethereisvariabilitywithbothmethods;therefore,itdoesnotappearthatH2O2isaninterferenttotheIC. L!"   TheH2O2levelwasthenincreasedtofivetimestheMethod7levelto "$ conformwiththeASTMmethod.FiveadditionalsetsofsamplesweretakencontainingNOxandSO2,andsixsetsofsamplesweretakencontainingonlyNOx.  $D& Table4showstheresultsofthesamplesanalyzedbyMethods7and7A,andTable5showstheresultsoftheremainingsetsofdataanalyzedbyMethod7A.theresultsinTables4and5indicatebetterabsorptionwithincreasedH2O2 &T) solutionwhenSO2ispresent.TheresultsinTables4and5showthatthe &* setswithonlyNOxareconsistentlylowerthanthesetscontainingNOxandSO2. |'+ Theanalysesalsoindicatethatbothmethodsdidnotyieldacceptableresults.  ,(d, P| @ TABLE1.DeterminationofSO2Interference 0 *q ddd Xdd Xdd X(#(#q,ddU,tdU,tdU,tde+  / " ` }/SO2conc.,   ppm 9 *x H"  9M7ANOx   conc.,ppm 9 *x H"  9ActualNOx    conc.,ppm 9 *x H "  9Percentdiff.fromact.NOxconc. O B*x H" }   rO6648231033105011121142 0 !   0326305225279237256 0 !   0360319223303261268 0 !    0Є9̄5+0.5̄8̄9̄5 F 9! & r   rF152717121735205920824436 0 ! ,  025520721219218027.4 0 ! 2  024519223320016526.3 0 ! 8  0+4_8̄9̄4+9+4 F 9! > r   rF265931353389361147694769 0 !p@D  011338.477.867.563.442.3 0 !p@J  011812093.610581.982.9 0 !p@P  0Є3̄68̄17̄36̄23̄49 F 9!p@V r   rF213223122836308046825366 0 !\  094.963.792.21296831 0 !b  019019412814112188.4 0 !h  0Є50̄52̄50̄8̄44̄65 J 9!n r   J26313044 2 !p  211286.6 2 !r  2148129 2 !t  2Є35̄331'%v      1  v @ TABLE2.Methods7ASampleswithFourTimesH2O2 0 * ddddUtdUtdUtde (#(#,ddU,tdU,tdU,tde+  / " ` }/SO2conc.,   ppm 9 *x H"  9M7ANOx   conc.,ppm 9 *x H"  9ActualNOx    conc.,ppm 9 *x H "  9Percentdiff.fromact.NOxconc. S B*x H" }   4S2953285322493649 2 !   2132170139145 2 !   2163131145125 2 !   2Є19̄29+5̄161'%   4    1@Z Z TABLE3.Methods7and7ASampleswithFourTimesH2O2 p $ * ddddUtdUtdUtde(#(#,ddU,FtdR,Ftd5,tdE,ttd5,td5+  / "  & $/SO2conc., 8( ppm 9 *)"  9M7ANOx 8+ conc.,ppm 9 *,"  9ActualNOx 8. conc.,ppm 9 */"  9Percentdiff.fromact.NOxconc. 9 *h3"  9M7NOx 6 conc.,ppm 9 *h7"  9Percentdiff.fromact.NOxconc. S B*h;" $   S244723413464299228772663 2 !@A  2189193111138158128 2 !@G  217917395.4135147171 2 !@M  2+6+12+16+2+7̄25 2 !@S  220211960.7160151129 2 !@Y  2+13̄31̄36+18+3̄241'%@_      1  _ @Z Z TABLE4.Methods7and7ASampleswithFiveTimesH2O2 0 * d,ddU,FtdR,Ftd5,tdE,td5,td5+  % %SO2conc.,ppm  M7ANOxconc.,ppm  ActualNOxconc.,ppm  Percentdiff.fromact.NOxconc.(M7A)  M7NOxconc.,ppm  Percentdiff.fromact.NOxconc.(M7) % %27612807238724142376  142134145180168  154144165189191  Є8̄7̄12̄4.6̄12  132lost168143162  Є14̈+1.7̄24̄15 ) )0*0000  157148150149154  179185186186182  Є13̄20̄19̄20̄16  11397.6164144168  Є37̄47̄12̄22̄7*Acolorimetricanalysisfornitriteindicatednonitritewaspresent.@.. TABLE5.Method7ASampleswithFiveTimesH2O2* d,ddU,tdU,tdU,tde+  % }%SO2conc.,ppm  M7ANOxconc.,ppm  ActuaNOxconc.,ppm  Percentdiff.fromact.NOxconc. % r%265725322771276629792553  175143138118145197  159153138124148194  +10̄7̄0.5̄5̄2+1 % r%244628483288304633222355  157138119116106206  14812511010997.7201  +6+9+9+6+8+2 % r%000000  377341363343401382  403345401400419418  Є7̄1̄9̄14̄4̄9 % r%000000  335381366367385401  361397391394412417  Є7̄4̄7̄7̄7̄4 % 4%2784265526632010  170173162198  160156131192  +7+11+24+3 % %00000  345289282320326  379371351347400  Є10̄22̄20̄8̄19 ) )00000  203162186161198  186161134172182  +10+0.3+39+6+9..Theproblemwithprecisionandaccuracymaybeduetotheformationofnitrousoxide(N2O).AstudyperformedbytheAirandEnergyEngineeringResearchLaboratoryindicatesthatNOmaybeconvertedtoN2OwheninthepresenceofSO2andmoisture.TheN2Owouldnotbeabsorbedintothesolutionnordetected.However,theproblemwiththefivetimesH2O2solutionoccurswhennoSO2ispresent. CONCLUSION ..Inconclusion,thislaboratoryevaluationindicatesthatSO2beginstointerferewithMethod7AatSO2levelsabout2100ppm.TheMethod7A(andMethod7)absorbingsolutionwithaH2O2concentrationfivetimesitscurrentstrengthappearstocompensatefortheSO2interference.However,aconsistentlylowbiasoccurswhenonlyNOxissampledandisapparentlyduetotheincreasedH2O2concentration. RECOMMENDATIONS ..SinceN2Owillnotbeabsorbedintosolution,thenincreasingtheH2O2intheabsorbingsolutionwillnotbeeffective.IfconversiontoN2Oisaproblem,aninstrumentalmethodmaybeneeded.ItisrecommendedthatfurthertestingshouldbeperformedinordertoestablishtheexactlevelofSO2thatcausesinterferenceandwhentheregularMethod7solutionshouldbeused,andtodetermineifthereisconversiontoN2O.