Measurements made from the DOE G-1 aircraft were used to calculate the rate and efficiency of O{sub 3} production downwind of an isolated, coal-fired power plant. The plume was transected 12 times at distances ranging to 65 km from its source (corresponding to an age of {approx}4 h assuming constant wind velocity). For NO{sub x}, a loss rate of 0.5 h{sup -1} was calculated. If reaction with OH was the sole loss mechanism, then an [OH] = 1.6 x 10{sup 7}molec/cm{sup 3} is inferred, which is {approx}2-3X values calculated using a box model constrained by observations. Possible explanations for this discrepancy are discussed. O{sub 3} production per molecule of NO{sub x} approached 6-8 after the plume had aged &gt;3h. Peak O{sub 3} concentrations were 15 ppbv above background. Dilution appears to limit the peak O{sub 3} concentration despite the high production efficiency. Hydrocarbon samples indicate high levels of VOC reactivity ({approx}8 s{sup -1}) in the plume. The number concentration of accumulation mode particles increases significantly with plume age indicating a rapid formation of aerosol mass

Brechtel, F.

Daum, P. H.

Kleinman, L. I.

Lee, Y. N.

Nunnermacker, L. J.

Springston, S. R.

Weinstein-Lloyd, J.

UNT Digital Library

BNL-68694Research by BNL investigators was performed under the auspices of the U.S. Departmentof Energy under Contract No. DE-AC02-98CH10886.CHEMICAL EVOLUTION OF A POWER-PLANT PLUMES. R. Springston1, L. I. Kleinman, F. Brechtel, P. H. Daum,Y.-N. Lee, L. J. Nunnermacker, and J. Weinstein-Lloyd2Atmospheric Sciences DivisionBrookhaven National LaboratoryUpton, NY  11973-5000October 2001For presentation at theAmerican Meteorological Society 82nd Annual Meeting,Orlando, FLJanuary 13-17, 2002*  Corresponding author address: Atmospheric Sciences Division, Building 815E, Brookhaven NationalLaboratory, Upton, NY 11973; e-mail: srs@bnl.gov.2  Department of Chemistry and Physics, SUNY, Old Westbury.P1.29 CHEMICAL EVOLUTION OF A POWER-PLANT PLUMEStephen R. Springston*, L.I. Kleinman, F. Brechtel, P.H. Daum, Y.-N. Lee, L.J. Nunnermacker and J. Weinstein-LloydBrookhaven National Laboratory, Upton, NY 11973-50001. INTRODUCTIONDuring the Texas 2000 Air Quality Study (TexAQS2000), the DOE G-1 research aircraft was used tocharacterize pollutant distributions in and around thegreater Houston metropolitan area.  These measurementswere part of a large cooperative effort designed tounderstand the factors controlling the formation, transportand fate of air pollutants in this region.  The high densityof pollutant sources related to transportation, industrialpetrochemical processing and power generationcomplicate the assessment of individual contributions tothe overall air quality.  Sampling from isolated sources inthe region is one approach to studying differencesbetween these sources and the subsequenttransformations of their atmospheric discharges.  2. OBSERVATIONSThe G-1 flew twenty sampling missions duringTexAQS 2000.  These flights were primarily flown withina ~90-km distance from the center of Houston.  One flightwas devoted to study the processing of stack emissionsfrom an isolated power-plant plume well removed fromurban influences. 2.1 Source CharacteristicsThe Sandow power plant, located in Milam County,TX,  consists of three 125-MW electrical generation unitsbuilt in the 1950's and a fourth 545-MW unit constructedin 1981.  The four units provide power for a co-locatedaluminum smelter with excess power from Unit 4 added tothe commercial grid.  The site is located next to Sandowmine which supplies lignite coal for the boilers.  Emissionlevels from 1999 are shown in TABLE 1.TABLE 1SO2 NOx CO PM10 NMOC(ktons/y)G Units 1-3 61 20 22 1.3 1.6Unit 4 29 9 1 1.0 0.1Total 90 29 23 2.3 1.71999 TNRCC, Point Source Emission Inventory2.2 Sampling ConditionsThe research flight was conducted on September 10,2000, a day following widespread precipitation and the airwas relatively clean upwind from the source.  Beginningat 14:30 local standard time, the aircraft repeatedlytransected the plume for ~1 h at downwind distances from<4 to 65 km.  Based on an average wind speed of 4 m/s,as measured aloft, the plume age when sampled rangedfrom ~10 min to ~4 h.  Winds in the plume region weresteady from the SE during the sampling period.  Aconstant altitude of 580 m (MSL) or ~435 m (AGL) wasmaintained while tracking the plume.  At 65-km downwind,the aircraft returned to the plant while climbing steadily.The mixing layer height at that time was 1800 m (MSL) or1650 m (AGL) as marked by scattered cumulus cloudsand a slight increase in potential temperature. 2.3 MeasurementsSpecies measured included O3, NO, NO2, NOy, CO,SO2, speciated VOC (canister samples analyzed at YorkUniversity), H2O2, organic peroxides (Zheng et al., 2001),formaldehyde (Lee et al., 1998), a full range of aerosolsize spectra between 3 nm - 16 :m (Buzorius et al.,2001), aerosol chemical composition (Lee et al., 2001)and meteorological parameters.  O3 and SO2 weremeasured by commercial instruments modified to achieveresponse times of ~10 s.  Nitrogen species weremeasured with a three-channel chemiluminescentinstrument.  NO2 was converted to NO by UV photolysis.NOy  was converted to NO by a Mo catalyst heated to350oC and mounted externally in the free airstream. Theresponse time for the three channels was <4 s.  VOCcanisters took ~45 s to fill.  Measurements made from theG-1 for the entire TexAQS 2000 and ancillary materialsa re  ava i lab le  by  anonymous  f tp  f rom:ftp://aerosol.das.bnl.gov/pub/Houston00/.3. RESULTS AND DISCUSSIONThe spatial distribution of the plume shown in Fig. 1was generated by the two-dimensional interpolation ofSO2 data measured along the flight track.* Corresponding author address:  Stephen R.Springston, Brookhaven National Laboratory,Atmospheric Sciences Division, Bldg. 815E, PO Box5000, Upton, NY 11973-5000; e-mail: srs@bnl.gov.31.131.030.930.830.730.6Latitude (deg)-97.6 -97.4 -97.2 -97.0 -96.8Longitude (deg)SO20.10.20.5125102050ppbv Flight TrackFigure 1  Plume visualization from SO2 signal. The meandering nature of the plume apparent in Fig. 1 isdue to changes in the wind field over time.  The edges ofthe plume are clearly identified as the concentration ofSO2 reached background levels (<0.2 ppbv) at the endsof each transect.  Gridding of flight-track data, as shownin Fig. 1, also allows interpolation to span short periods ofmissing data arising from instrument zeros or calibrations.The plume changes direction at a latitude of ~30.8 N.This is consistent with a change in wind direction roughly2 hours earlier.  Beyond this point the cross-plumeintegrated values of SO2 and NOy decrease markedly.  Itappears that after a plume age of ~2 hours, the transectsare following only a portion of the original plume.  Possiblereasons for this include venting out of the boundary layerand/or shearing of the plume away from the samplingaltitude.  In the absence of vertical sampling data, thethree-dimensional flow cannot be definitivelycharacterized.  3.1 Gaseous SpeciesVertical dispersion through diffusion and advectionmakes absolute quantitative analysis of componentsproblematic.  The consistent ratio of SO2 to NOy over a4-h period as shown in Fig. 2 is used as one indication ofmeasurement validity.  43210Slope [SO2]  vs  [NOy]43210Plume Age (h)(error bars at ± 3 σ)Figure 2  Relative plume composition over 4 h oftransport.SO2 is removed from the plume by oxidation tosulfate, but at time scales longer than 4 h.  NOy is anaggregate measurement of all odd-nitrogen species.  Therelative concentrations of individual NOy componentschange as NO is photochemically processed, ultimatelyforming HNO3.  Over 90% of the NOx emitted is oxidizedduring the 4 hours studied.  Loss of HNO3 due to drydeposition is minimal in a 4-h period, thus the total NOy inthe plume should remain constant.  As expected, the ratioof SO2 to total NOy is shown to be roughly constant overthe age of the plume in Fig. 2.  The weighted mean of SO2to NOy is 2.7 (F=0.3).  This measured value is consistentwith a molar ratio of 2.1 calculated from TABLE 1 giventhe variabilities introduced by the implementation ofemissions controls, day-to-day boiler conditions andinventory uncertainties.  The ratio of NOx to total NOy  decreases as the plumeages and is used as an indicator of the plume’sphotochemical age.  For each transect, the slope of NOxvs NOy is plotted in Fig. 3.  1.21.00.80.60.40.20.0Slope of NOx vs NOy43210Plume Age (h)(error bars at ±3σ)Figure 3  Photochemical processing consumes NOx asa fraction of total NOy.The data of Fig. 3 indicate a loss rate for NOx of ~0.5 h-1.This is consistent with a loss rate of ~0.4 h-1 reported fora Nashville, TN power plant (Nunnermacker et al., 2001).If the loss of NOx is due solely to the reaction of NO2 withOH, then [OH] = 1.6x107 molec/cm3.  This value is roughly3X [OH] calculated  using a constrained steady state(CSS) photochemical box model (Kleinman et al., 2001).This discrepancy has several possible explanations.  First,total processing time may be as much as 50% longer thanindicated in Fig. 3, as wind speeds generally increase inthe afternoon.  Processing time was calculated usingwinds measured at the time of sampling. On this day,Continuous Air Monitoring Station (CAMS) sites in theregion show a moderate increase in surface wind speed(TNRCC, 2001) in the hours prior to sampling.  Second,appreciable photochemical processing occurred at timescloser to solar noon than reflected in the modelcalculations which used the local sampling time.  A thirdreason for the discrepancy may  be the loss of NOxthrough other channels  involving organic nitrates andPAN.  The relative magnitudes of these effects are beingstudied.The O3 production efficiency is an estimate of the O3produced per NOx consumed (Trainer et al., 1993;Olszyna et al., 1994;  Daum et al., 2000).  At eachtransect, this is calculated from the slope of Ox vs. NOz asshown in Fig. 4 (where [Ox] = [O3] + [NO2]). 86420Slope of Ox vs NOz43210Plume Age (h)(error bars at ±3σ)Figure 4  O3 production efficiency increases with plumeage.  The efficiency increases with plume age to a final level of~6.  This efficiency is consistent with that reported for apower plant in Nashville (Ryerson et al., 2001).   Althoughboth the production efficiency and the concentration ofNOx are quite high in this plume, the overall increase in O3is relatively modest.  After 4 h, the O3 concentration in theplume is ~15 ppbv above background levels.  We ascribethe limited increase to dilution of the plume as it waftsdownwind.Three hydrocarbon samples were acquired in andaround the plume region.  Two different reactivities werecalculated for each sample, a total reactivity forOH + VOC and a second reactivity including only biogenichydrocarbons.  As expected, the background samplesexhibited low reactivities (ktotal= 0.37 s-1, kbiogenic=0.13 s-1).The sole sample taken within the plume showed bothelevated OH total reactivity (ktotal= 8.2 s-1), and elevatedreactivity from species not associated with a power-plantplume (kbiogenic= 3.8 s-1).  The in-plume VOC sample wastaken at a plume age of ~2h by which time appreciabledilution had reduced the NOx concentration to 2-3 ppbv.The plume at this point has high VOC reactivity and lowNOx concentration leading to NOx limited O3 production.The presence of biogenic species in the plume cannot beexplained by direct stack emissions.  Entrainment ofhydrocarbon-rich air near the surface is suggested as apossible explanation for this observation.3.2 ParticulatesThe increase in particle concentrations wasparticularly striking.  The absolute concentration ofaccumulation-mode particles (0.1 - 3 :m) increased by afactor of two over the course of the plume.  Over thissame distance, the concentration of SO2 at the center linedecreased by ~2 orders of magnitude.  SO2 is assumed tobe a conservative tracer and its decrease in concentrationis thereby a measure of dilution.  When normalized fordilution, the relative concentration of accumulation-modeaerosol particles increases by more than a factor of 200as shown in Fig. 5.300250200150100500Accumulation Mode (Rel. Conc.)43210Plume Age (h)Figure 5  Increase in particles with plume age.  Totalaccumulation mode (PCASP) normalized to SO2concentrations to remove the effects of dilution. Particles dominated by sizes < 0.4 :m.4. CONCLUSIONSMeasurements made from the DOE G-1 aircraft wereused to calculate the rate and efficiency of O3  productiondownwind of an isolated, coal-fired power plant.  Theplume was transected 12 times at distances ranging to 65km from its source (corresponding to an age of ~4 hassuming constant wind velocity).  For NOx, a loss rate of0.5 h-1 was calculated.  If reaction with OH was the soleloss  mechanism, then an [OH] = 1.6 x 107 molec/cm3 isinferred, which is ~2 - 3X  values calculated using a boxmodel constrained by observations.  Possibleexplanations for this discrepancy are discussed.  O3production per molecule of NOx approached 6-8 after theplume had aged >3h.  Peak O3 concentrations were 15ppbv above background.   Dilution appears to limit thepeak O3 concentration despite the high productionefficiency.  Hydrocarbon samples indicate high levels ofVOC reactivity (~8 s-1) in the plume.  The numberconcentration of accumulation mode particles increasessignificantly with plume age indicating a rapid formation ofaerosol mass. 5. ACKNOWLEDGMENTSWe are indebted to the pilots and flight crew of theDOE G-1 for safe operations.  Special acknowledgmentis due chief pilot Bob Hannigan, whose navigation skillsand positional awareness enabled accurate tracing of thisplume.  The Atmospheric Chemistry Program supportedthis research as performed under the auspices of the U.S.Department of Energy under contract DE-AC02-98CH10886.6. REFERENCESBuzorius, G., Brechtel, F., Zelenyuk, A., Imre, D.,Angevine, W.M., 2001:  Observations of recent newparticle formation in Houston during TexAQS-2000.Fourth Conference on Atmospheric Chemistry.Amer. Meteor. Soc., Orlando, Fl, Poster P1.21.Daum, P.H., Kleinman, L.I., Imre, D.G., Nunnermacker,L.J., Lee, Y.-N., Springston, S.R., Newman, L., 2000:Analysis of the processing of Nashville urbanemissions on July 3 and July 18, 1995.  J. Geophys.Res., 105, 9107-9119.Gillani, N.V., Meagher, J.F., Valente, R.J., Imhoff, R.E.,Tanner, R.L., Luria, M., 1998:  Relative production ofozone and nitrates in urban and rural power plantplumes 1.  Composite results based on data from 10field measurement days.  J. Geophys. Res., 103,22593-22615.Kleinman, L.I., Daum, P.H., Lee, Y.-N., Nunnermacker,L.J., Springston, S.R., Weinstein-Lloyd, J., Rudolph,J., 2001:  Sensitivity of ozone production rate toozone precursors.  Geophys. Res. Lett., 28, 2903-2906.Lee, Y.-N., Zhou, X., Kleinman, L.I., Nunnermacker, L.J.,Springston, S.R., Daum, P.H., Newman, L., Keigley,W.G., Holdren, M.W., Spicer, C.W., Young, V., Fu,B., Parrish, D.D., Holloway, J., Williams, J., Roberts,J.M., Ryerson, T.B., Fehsenfeld, F.C., 1998:Atmospheric chemistry and distribution offormaldehyde and several multioxygenated carbonylcompounds during the 1995 Nashville/MiddleTennessee Ozone Study.  J. Geophys. Res., 103,22449-22462.Lee, Y.-N., Song, Z., Liu, Y., Daum, P., Weber, R., Orsini,D., Laulainen, N., Hubbe, J., Morris, V., 2001:Aerosol chemical characterization on board the DOEG1 aircraft using a Particle-into-Liquid Sampler(PILS) during the TexAQS 2000 Experiment.  FourthConference on Atmospheric Chemistry.  Amer.Meteor. Soc., Orlando, Fl, Paper 10.13.Nunnermacker, L.J., Kleinman, L.I., Imre, D., Daum, P.H.,Lee, Y.-N., Lee, J.H., Springston, S.R., Newman, L.,Gillani, N., 2001:  NOy lifetimes and O3 productionefficiencies in urban and power plant plumes:Analysis of field data.  J. Geophys. Res., 105, 9165-9176.Olszyna, K.J., Bailey, E.M., Simonaitis, R., Meagher, J.F.,1994:  O3 and NOy relationships at a rural site.  J.Geophys. Res., 99, 14557-14563.Ryerson, T.B., Trainer, M., Holloway, J.S., Parrish, D.D.,Huey, L.G., Sueper, D.T., Frost, G.J., Donnelly, S.G.,Schauffler, S., Atlas, E.L., Kuster, W.C., Goldan,P.D., Hubler, G., Meagher, J.F., Fehsenfeld, F.C.,2001:  Observations of ozone formation in powerplant plumes and implications for ozone controlstrategies.  Science, 292, 719-723.TNRCC, 2001:  Continuous Air Monitoring Site web site.http://www.tnrcc.state.tx.us/cgi-bin/monops/daily_summary.Trainer, M., Parrish, D.D., Buhr, M.P., Norton, R.B.,Fehsenfeld, F.C., Anlauf, K.G., Bottenheim, J.W.,Tang, Y.Z., Wiebe, H.A., Roberts, J.M., Tanner, R.L.,Newman, L., Bowersox, V.C., Meagher, J.F.,Olszyna, K.J., Rodgers, M.O., Wang, T., Berresheim,H., Demerjian, K.L., Roychowdhury, U.K., 1993:Correlation of ozone with NOy in photochemicallyaged air.  J. Geophys. Res., 98, 2917-2925.Zheng, J., Alaouie, A., Weinstein-Lloyd, J., Springston,S., Nunnermacker, L., Lee, Y.-N., Brechtel, F.,Kleinman, L., Daum, P., 2001:  Measurement ofhydroperoxides during the Texas 2000 Air QualityStudy.  Fourth Conference on AtmosphericChemistry.  Amer. Meteor. Soc., Orlando, Fl, PosterP1.22.

Chemical Evolution of a Power-Plant Plume

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Chemical Evolution of a Power-Plant Plume

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