Volatile Organic Compound Emissions from Dairy Cows and Their Waste as Measured by Proton-Transfer-Reaction Mass Spectrometry

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1 Voltile Orgnic Compound Emissions from Diry Cows nd Their Wste s Mesured by Proton-Trnsfer-Rection Mss Spectrometry STEPHANIE L. SHAW,*, FRANK M. MITLOEHNER, WENDI JACKSON, EDWARD J. DEPETERS, JAMES G. FADEL, PETER H. ROBINSON, RUPERT HOLZINGER,, AND ALLEN H. GOLDSTEIN Deprtment of Environmentl Science, Policy, nd Mngement, University of Cliforni, Berkeley, Hilgrd Hll, Berkeley, Cliforni 94720, nd Deprtment of Animl Science, University of Cliforni, Dvis, Dvis, Cliforni Cliforni diries house pproximtely 1.8 million lctting nd 1.5 million dry cows nd heifers. Stte ir regultory gencies view these diries s mjor ir pollutnt source, but emissions dt re sprse, prticulrly for voltile orgnic compounds (VOCs). The objective of this work ws to determine VOC emissions from lctting nd dry diry cows nd their wste using n environmentl chmber. Crbon dioxide nd methne were mesured to provide context for the VOCs. VOCs were mesured by proton-trnsferrection mss spectrometry (PTR-MS). The compounds with highest fluxes when cows plus wste were present were methnol, cetone + propnl, dimethylsulfide, nd m/z 109 (likely 4-methyl-phenol). The compounds with highest fluxes from fresh wste (urine nd feces) were methnol, m/z 109, nd m/z 60 (likely trimethylmine). Ethnol fluxes re reported qulittively, nd severl VOCs tht were likely emitted (formldehyde, methylmine, dimethylmine) were not detectble by PTR-MS. The sum of rective VOC fluxes mesured when cows were present ws fctor of 6-10 less thn estimtes historiclly used for regultory purposes. In ddition, ozone formtion potentils of the dominnt VOCs were 10% those of typicl combustion or biogenic VOCs. Thus diry cttle hve comprtively smll impct on ozone formtion per VOC mss emitted. Introduction The Sn Joquin Vlley (SJV) in centrl Cliforni is in extreme nonttinment of current stte nd federl ozone (O 3) stndrds (1). O 3 is formed by the interction of sunlight with voltile orgnic compounds (VOCs) nd nitrogen oxides. * Corresponding uthor phone: (510) ; fx: (510) ; e-mil: slshw@lum.mit.edu. University of Cliforni, Berkeley. University of Cliforni, Dvis Current ddress: Institute for Mrine nd Atmospheric Reserch (IMAU), Utrecht, The Netherlnds. VOC emissions reductions re required t the ir district level to chieve O 3 stndrd ttinment. Agriculturl processes, notbly niml opertions, re no longer exempt from emission controls s result of Cliforni Sente Bill 700. The proposed SJV Air District Rule 4570 intends to reduce VOC emissions from diries, cttle feedlots, poultry rnches, nd other opertions by 14 Mg VOC dy -1 (26%; 2). Rule 4570 development is ongoing, includes the doption of VOC emission fctors, nd is scheduled to be implemented in Jnury Cliforni is home to the lrgest diry industry in the world, with 2100 diries tht produce 23% of the ntion s milk supply. Within the lst 10 yers the number of lctting cows per diry hs more thn doubled to n verge of 825. In 2004 Cliforni diry cttle nd their wste were estimted to contribute s much rective orgnic gses (ROGs) to the tmosphere s light/medium duty trucks or light pssenger vehicles (2). ROGs re defined s the subset of VOCs tht re rective enough to contribute substntilly to tmospheric photochemistry (1). The relevnt 183 µg ROG cow -1 s -1 emission fctor ws bsed on 67-yer-old study of wht is now known to be totl orgnic gs emissions from dult Holstein nd Jersey cows (3). ROG emissions were then clculted by pplying n 8% fctor s determined by the Environmentl Protection Agency (4). Compound-specific VOC nlysis techniques hve improved drmticlly in recent yers, nd new mesurements of diry emissions re required to crete ccurte inventories. This rticle reports the results of controlled chmber experiments designed to identify nd quntify VOC emissions from diry cows nd their wste t vrious stges of the lcttion cycle (SLC). Emissions were mesured with proton-trnsfer-rection mss spectrometer (PTR-MS). In contrst to trditionl gs chromtogrphy-mss spectrometry, this technique uses soft chemicl ioniztion which results in miniml compound frgmenttion. Therefore no seprtion is required, resulting in high frequency mesurements nd rpid response times (s) (5). In ddition, simultneous detection of vriety of VOC types tht trditionlly required multiple instruments is possible. Methods Site Description. Experiments were conducted t the University of Cliforni, Dvis, Deprtment of Animl Science Swine Reserch Fcility. Groups of three cows ech were housed in n environmentlly controlled chmber (4.4 m 2.8 m 10.5 m) t 18 C, which simulted representtive commercil freestll conditions. Fresh ir ws provided by forced ventiltion t L min -1, resulting in chmber residence time of 6 min. Tests of smoke relese with complete dispersl throughout the chmber prior to execution of the experiments showed the ir ws completely clered in <10 min. Feed nd wter troughs were provided to llow d libitum consumption. The cows excreted urine nd feces, which ccumulted on the concrete floor until the chmber ws clened. Therefore ll reported cow mesurements lso include wste. All wste only mesurements re pplicble for fresh dy-old wstes. Teflon diphrgm (oil-less) pumps (KNF) pulled ir t controlled rte (MKS Instruments) from inlet nd outlet vents on the chmber ceiling to nlyticl instrumenttion in n djcent chmber. All smpling lines were pproximtely 20 m long 1/8 in. ID Teflon tubes with inline Teflon prticulte filters. A1Lmin -1 flow ws pulled from the chmber to proton-trnsfer-rection mss spectrometer (Ionicon Anlytik) chnnel, of which minor frction ws nlyzed. A /es061475e CCC: $37.00 xxxx Americn Chemicl Society VOL. xx, NO. xx, xxxx / ENVIRON. SCI. & TECHNOL. 9 A Published on Web 01/13/2007 PAGE EST: 6.1

2 TABLE 1. Diet Composition (in % of Dry Mtter (DM)), DM Ingested, Milk Yield, nd Body Weight for Cows in Vrious Stges of Lcttion Cycle ingredient fr off close up erly lcttion mid lcttion 1 mid lcttion 2 lte lcttion grin mix b lflf ot hy whole cottonseed mel lmond hulls soyben mel milk minerl energy II slt ots nicin pellet nutri-chlor dry cow pellet c totl DM ingested NA NA (DMI; kg cow -1 time -1 d ) verge milk yield (kg cow -1 dy -1 ) verge body weight (kg cow -1 ) Mid lction 1 fed the sme diet s erly lcttion; mid lcttion 2 fed the sme diet s lte lcttion. b The grin mix contined (% DM) brley (41.5), corn (41.5), beet pulp (13.8), nd tllow (3.2). c The dry cow pellet contined (% DM) minerls (27), soyben mel (36.5), nd whet mel run (36.5). d DMI for lctting cows is clculted for the 6 h enclosure time nd is only portion of the dily intke. DMI for dry cows is per 24 h enclosure time. L min -1 flow ws pulled to second chnnel nd split between LICOR 6262 infrred gs nlyzer, to mesure CO 2, nd cvity-enhnced-bsorption spectrometer (Los Gtos Reserch, Inc.), to mesure CH 4. Animl Mngement. Both dry (nonlctting) nd lctting Holstein diry cows were used. Dry cows were pregnnt nd either fr off (45-60 dys) or close up (e14 dys) from clving. Lctting cows were ctegorized s erly, mid, or lte bsed on the dys from clving nd milk yield. Diet composition nd consumption re listed in Tble 1 nd were intended to represent diets fed on commercil diries in Cliforni. The fr off diet ws predomintely forge bsed nd provided sufficient energy nd nutrients for cow mintennce nd fetl development. The close up diet included forge nd concentrte, which provided dditionl energy nd nutrients for fetl development, s well s strch nd sugr to increse the mylolytic microorgnisms. This prepred the cows to lter receive the erly lcttion diet (high concentrte). The lte lcttion diet contined more forge nd less ft since the energy requirements for milk synthesis decline s yield decreses. Mid lcttion cow groups were split in two nd fed either erly or lte lcttion diets to determine if composition influenced emissions. Cow groups were selected ccording to one of these six SLC. Three dry cows entered the empty chmber t pproximtely 08: 30, nd they remined for two consecutive 24 h smpling periods. The chmber ws clened with pressure hose t hour 24 to remove ccumulted wste while the cows remined inside. Cows were removed fter 48 h, but the ccumulted wste from hours h remined nd ws smpled for nother 24 h. Alterntively, three lctting cows were milked before entry into the chmber t 08:30, where they remined for 6 h before removl for second milking. Two to four consecutive dys of lctting cows were tested. These consecutive dys ech hd either different cow groups or replicte testing of the sme group. Accumulted wste from the previous dy ws smpled for 24 h period fter some of the lctting cow groups exited. All mesurements were repeted t lest twice. Animl cre ws reviewed nd pproved by the Institutionl Animl Cre nd Use Committee t the University of Cliforni, Dvis. Gs Anlysis. The PTR-MS uses chemicl ioniztion with H 3O + s rectnt nd proton donor. If the trget VOC hs proton ffinity (PA) greter thn tht of H 2O, the proton is trnsferred to the VOC, which is detected by mss spectrometer. Proton trnsfer occurs on every collision of H 3O + ion with VOC molecule, whenever PA VOC > PA H2O, thus defining the rection rte. An pplied electricl field defines the ion rection time. VOC concentrtions re clculted by combining these with mesured count rtes of H 3O + nd the protonted VOC, which re modified by experimentlly determined mss spectrometer trnsmissions t ech m/z rtio (5). Therefore the PTR-MS llows estimtion of mixing rtios for species which re unidentified or for which clibrtion stndrds were not vilble (5), which is n importnt benefit for these mesurements. Mny VOC types, including lcohols, ldehydes, romtics, ketones, lkenes, mines, nitriles, sulfides, nd cids, hve PA > PA H2O. Alknes, some lkenes, nd hlogented compounds re not detected. The PTR-MS lso provides much more ccurte mesurements for polr VOC (e.g., ldehydes or ketones) thn ny technique requiring smple storge (e.g., cnisters (6)). Compound detection limits re extremely low t pptv, even in complex gs mixes. Tenttive identifictions of protonted VOC msses were mde by comprison with published mbient or diry mesurements (e.g., 5, 7-10). Confirmtion occurred through nlysis of frgmenttion, wter cluster, nd isotope ptterns in the context of ech experiment, s few msses re unique to single compound. As with ll nlyses, VOCs tht tend to dsorb or condense onto surfces cn be difficult to detect. Anlyticl cpbilities for such VOC (i.e., trimethylmine (TMA), voltile ftty cids (VFA), phenols) must be determined on n instrumenttion bsis. As clibrtion stndrds with which to test for TMA nd VFA losses were not vilble, the observed fluxes of these compounds must be considered lower limits. They re included for reltive comprisons cross cow groups. Previous work with the identicl PTR-MS showed good sensitivity nd negligible memory effects for cetic cid (7). Expected compounds tht typiclly cnnot be quntified with the PTR-MS re hydrogen sulfide (H 2S), crbon disulfide, nd formldehyde due to low PA, nd methylmine (MA) nd dimethylmine (DMA) due to high instrument bckground t their msses. In ddition, lrge frction of smpled ethnol is frgmented nd converted to B 9 ENVIRON. SCI. & TECHNOL. / VOL. xx, NO. xx, xxxx

3 TABLE 2. Averge ( 1σ of All Hourly Averged Compound Fluxes (µg cow -1 s -1 ) from the First 6hofEnclosure for All Replicte Dys (n) cow CO 2 cetic cetone + groups 10-4 TOG b CH 4 ROG c methnol d DMS d m109 d cid d propnl e fr off 21, n ) ( 1.2 NA NA ( ( ( ( ( 1.0 fr off f 86, n ) ( 1.5 NA NA ( ( ( ( ( 1.4 fr off WASTE f,g 0.17 ( 0.46 NA NA ( ( ( ( ( , n ) 2 close up 25, n ) ( ( ( ( ( ( ( 2.2 close up f 83, n ) ( ( ( ( ( ( ( 1.8 close up WASTE f,g 0.27 ( ( ( ( ( ( ( , n ) 2 erly lctting 24, n ) ( 2.1 NA NA ( ( ( ( ( 2.0 mid lctting 1 38, n ) ( 2.3 NA NA ( ( ( ( ( 1.8 mid lctting 2 17, n ) ( ( ( ( ( ( ( 1.3 mid lctting ( ( ( ( ( ( ( 0.07 WASTE g 12, n ) 2 lte lctting 14, n ) ( ( ( ( ( ( ( 0.64 lte lctting WASTE g 13, n ) ( ( ( ( ( ( ( 0.25 Number of dt points (first number) ws identicl for ll individul ROGs within cow group except m109 nd m60 ( 50%) nd CO 2 nd CH 4 ( 200%). b TOG ) CH 4 + ROG + cetone + propnl. c ROG ) sum of ll PTR-MS VOCs (except cetone + propnl, ethnol, nd TMA). d Msses included in ROG (nd thus TOG) with highest fluxes. e NOT included in ROG (but is TOG). f Dt from ll 24 h were used. g Fluxes relevnt for dy-old wste. ethene, which is undetectble due to low PA. This results in very low signl-to-noise for ethnol. The PTR-MS ws operted continuously, lternting between single ion mode (SIM) nd scn mode (SCAN) t the strt of ech smpling hour. SIM monitored 50 specified msses nd ws used to obtin better precision thn ws possible when monitoring msses mu in SCAN mode (Tble S1). SCAN mode ws useful for detecting ll compounds in tht mss rnge with PA > PA H2O. All msses observed by the PTR-MS re reported here unless noted otherwise. Twenty minutes ech of chmber inlet ir, outlet ir, nd inlet ir redirected through ctlytic converter to remove ll VOC nd crete n instrument blnk (7) were smpled hourly. Gseous clibrtion mixes (Apel-Riemer Environmentl, Inc.) were vilble for subset of the observed VOCs. Mixes were dded by dynmic dilution to the blnk for the lst 10 min of ech smpling hour. Uncertinties for clibrted compounds, determined s the difference between expected nd mesured concentrtions, were <(20% (Tble S1). Mesurement uncertinties for unidentified or unclibrted compounds were lrger (<(40%), s they were determined by propgting rection rte nd trnsmission uncertinties through the concentrtion clcultion. CO 2 concentrtions in chmber inlet ir were mesured during minutes nd of ech smpling hlf hour, while outlet ir ws mesured during the remining time. CO 2 ws clibrted three times dily for 2 min ech ginst two stndrds (2500 ( 50 ppm, nd either 386 ppm or 90 ppm). The cvity-enhnced-bsorption gs nlyzer mesured CH 4 concentrtions on this sme schedule. This instrument works in rel time, with ppbv detection limits, nd only occsionl fctory clibrtion is required (11). Fluxes were clculted s the concentrtion difference between the chmber outlet nd inlet ir strems, multiplied by the ir density nd flowrte, nd reported in units of µg compound cow -1 s -1. For this pper VOCs were defined s ll the individul voltile compounds detected by PTR-MS. Rective orgnic gses (ROGs) re the subset of VOCs tht contribute substntilly to tmospheric photochemistry nd form O 3 (1). This ws clculted s the sum of ll PTR-MS VOCs except cetone (exempt for regultory purposes (1)), TMA (unclibrted), nd ethnol (low signl-to-noise). Totl orgnic gses (TOGs) were clculted s the sum of CH 4, ROGs, nd cetone + propnl. VOC nd ROG dt were hourly verges ( points), nd ll other dt were hlf-hourly verges ( 100 points). Sttisticl Anlysis. The most bundnt compound fluxes from the different experiments were sttisticlly nlyzed with two models using PROC MIXED of SAS Version 9 (SAS Institute; Cry, NC). Model A compred different SLC when the cows plus wste were in the chmber nd included cow groups s rndom within SLC. The contrsts tested for model A were s follows: (1) ll lctting vs ll dry, (2) fr off vs close up, nd (3) erly vs lte lcttion diet groups. Model B included ll the terms of model A plus chmber sttus (empty chmber, cows plus wste, nd wste only) nd the interction of SLC nd chmber sttus. Chmber sttus ws compred only through the interction term. The contrsts tested for model B were s follows: (1) wste for lctting cows vs empty chmber, (2) wste for dry cows vs empty chmber, (3) cows plus wste vs wste for lctting cows, nd (4) cows plus wste vs wste for dry cows. Results nd Discussion CO 2 nd CH 4 Fluxes. CO 2 fluxes for the cow groups nd sttisticl comprisons between them re reported in Tbles 2 nd 3. Dry cows plus wste emitted significntly less CO 2 thn lctting cows plus wste. Fr off cows plus wste emitted significntly less CO 2 thn close up cows plus wste. However, the fluxes from vrious lctting cow groups were not significntly different from ech other, even though two different diets were used depending on the SLC. The fluxes verged cross ll dry nd ll lctting cows plus wste were (15.7 ( 3.9) 10 4 nd (19.4 ( 3.4) 10 4 µgco 2 cow -1 s -1, respectively. The corresponding dry nd lctting cow plus wste CH 4 fluxes were 3610 ( 860 nd 3900 ( 1000 µg cow -1 s -1.CH 4 fluxes from lctting cows re usully lrger thn those from dry cows becuse of greter feed consumption (3, 12). There ws no sttisticl difference between CH 4 fluxes in this study (P ) 0.13; 95% significnce) s determined with Student s t-test. This is likely due to the limited mount of vilble CH 4 dt. Fluxes were not mesured for fr off or erly lcttion cows, the former of which consumed substntilly less feed thn other cows (Tble 1). This lso prohibited CH 4 inclusion into the sttisticl models (Tble 3). CO 2 fluxes from wste were not significntly different from those in the empty chmber; both were smller thn those from the cows plus wste (Tble 3). CH 4 fluxes from the wste VOL. xx, NO. xx, xxxx / ENVIRON. SCI. & TECHNOL. 9 C

4 TABLE 3. Probbility (P) Vlues of the Differences between Averge Fluxes of Selected Comprisons CO 2 ROG methnol DMS m109 cetic cid cetone + propnl isoprene model A: cows + wste comprisons lctting vs dry b fr off vs close up b b erly vs lte lcttion diet groups model B: wste comprisons wste vs empty (lctting) < wste vs empty (dry) c < cows + wste vs wste (lctting) < < < cows + wste vs wste (dry) c < < Bold type signifies sttisticl differences with P < 0.05 (95% confidence). b Sttisticl differences exist with P < 0.10 (90% confidence). c Comprisons within groups of dry cows used verge fluxes from ll 24 h. All other comprisons were between dry nd lctting cows. As the ltter were only in the chmber for 6 h per dy, only the first 6hofdt were used (even when more existed). FIGURE 1. CO 2 nd CH 4 fluxes from close up cows nd their wste verged over both replicte 2.5 dy periods. Cow entry nd exit times re denoted by solid lines, clening by dshed line, nd clen nd empty chmber by E. Pooled stndrd errors re smller thn the symbols. of lctting cows were not different from (P ) 0.27; 95% significnce) those of the empty chmber s determined using Student s t-test, but fluxes from the wste of dry cows were (P < 0.001). Therefore CO 2 nd CH 4 were dominntly derived from the cows through respirtion nd enteric fermenttion, respectively. This ssumes the wste fluxes were representtive of those on the previous dy when the wste ws excreted. The exception ws CH 4 emission from the wste of dry cows. The verge CH 4 fluxes observed in this study were 1.8 times greter thn the 2123 µg cow -1 s -1 previously determined for dult Holstein nd Jersey cows (3, 4). Severl more recent mesurements were summrized by Willims et l. (13), who noted 2662 µg CH 4 cow -1 s -1 ws typicl for diry cows. This corresponds well with our 24-h-verged fluxes from close up cows plus wste. Furthermore, our CH 4 to CO 2 mss flux rtio (2.0%) ws 44% lower thn tht previously mesured for lctting Holstein cows (3.6%; (14)). Dily CO 2 nd CH 4 Ptterns. Figure 1 shows dily ptterns of CO 2 nd CH 4 fluxes from close up cows nd their wste. Fluxes of both compounds incresed immeditely fter the cows entered the chmber round 10:00 on the first dy. CH 4 fluxes peked bout 17:00 to 18:00 depending on the dy, nd then they decresed until 08:00 or 09:00 on subsequent mornings. Peks in CH 4 fluxes re commonly observed severl hours fter feeding (13). Thus the evening mxim for close up cows plus wste imply their primry mels were in the fternoons. The CO 2 pttern ws more subtle thn tht for CH 4, but still evident. However the CO 2 fluxes for fr off cows plus wste (not shown) were constnt over ech enclosure. This implies dily ptterns my chnge with SLC. Ptterns for lctting cows plus wste re unknown s they were in the chmbers for only 6 h per dy. However, Kinsmn et l. (14) reported tht CO 2 nd CH 4 fluxes from lctting Holsteins incresed t 07:00 nd decresed t 21:00. VOC Fluxes Mesured by PTR-MS. The VOCs or protonted msses mesured by the PTR-MS with highest fluxes from the cows plus wste re reported in Tble 2 nd were s follows: methnol (m/z ), cetone + propnl (m/z ), dimethylsulfide (DMS; m/z 63), m/z 109 (likely 4-methyl-phenol), m/z 60 (likely TMA), nd cetic cid (m/z ; possible minor contribution from propnol). There were mny VOCs with smll but clerly positive fluxes when the cows were present. The most bundnt of these were the following: m/z 41, cetldehyde (m/z 45), ethnol (m/z 47), m/z 49 (possibly methnethiol), m/z 58, m/z 64, isoprene (m/z 69), m/z (likely propionic cid), monoterpenes (m/z ), m/z 83 (possibly hexnl nd/or hexenol), m/z 87 (likely sum of pentnones), m/z (likely butyric cid + isobutyric cid + ethyl cette), dimethyldisulfide + phenol (m/z 95), m/z 101 (likely oxygented ldehydes or ketones), m/z (likely vleric cid + isovleric cid), m/z 107 (possibly benzldehyde + xylenes), m/z 121 (likely cetophenone), m/z 122, nd m/z 123. Diry cow emissions of similr suites of VOCs hve been previously observed. Dewhurst et l. (8) used vrition of the PTR-MS technique to mesure VOC in the rumen hedspce of Holstein-Friesin cows. They detected ppmv mounts of DMS nd ppbv mounts of ethnol, methnol, cetone, cetldehyde, cetic cid, propionic cid, butyric cid, nd propnol. These mesurements were often the sme order of mgnitude s our chmber ir concentrtions when cows were present. The verge DMS fluxes reported here compred well to previously published fluxes (2.4 µg cow -1 s -1 (13)). Some of the most bundnt VOCs we observed (methnol, ethnol, nd cetone) re lso the primry VOCs emitted in humn breth (15). The ROG fluxes verged cross ll dry nd ll lctting cows plus wste were 25 nd 23 µg cow -1 s -1, respectively. While ethnol ws not quntittive, it ws so bundnt its flux could be estimted s equl to, or slightly lrger thn, tht of methnol for ll experiments. Including this minimum ethnol estimte incresed the ROG fluxes to 40 nd 35 µg cow -1 s -1, for dry nd lctting cows plus wste, respectively. Regrdless of ethnol inclusion, TOG fluxes from both dry nd lctting cows plus wste were overwhelmingly dominted by CH 4 (>98%). After the cows were removed from the chmber their wste remined. The VOCs with lrgest fluxes emitted from ll wstes were methnol, m/z 109, nd m/z 60. Acetic cid fluxes from the wste of lctting cows were lso lrge (Tble 2). Hobbs et l. (9) mesured VOCs emitted from cttle D 9 ENVIRON. SCI. & TECHNOL. / VOL. xx, NO. xx, xxxx

5 FIGURE 2. VOC fluxes in µg cow -1 s -1 from dry cows verged over two replicte fr off nd two replicte close up cow periods. Cow entry nd exit times re denoted by solid lines, clening times by dshed lines, nd clen nd empty chmber by E. Pooled stndrd errors re smller thn the symbols except for methnol, which is depicted on one point in pnel A. mnure nd similrly found cetic cid nd 4-methyl-phenol (likely m/z 109) fluxes lrger thn those of other VFAs. No DMS, isoprene, or cetone + propnl fluxes were emitted from ny wste s there ws no significnt difference from the empty chmber fluxes (Tble 3). Therefore these compounds were likely derived only from the cows, ssuming the wste only fluxes re representtive of those from the previous dy. DMS ws previously reported to be derived from cows nd not their wste (13). The m/z 109 fluxes from wste were sttisticlly lrger thn those from the empty chmber. Interestingly, fluxes from the cows plus wste were sttisticlly smller thn those from wste lone (Tble 3). It is therefore not cler if m/z 109 ws derived in prt from the cows, or solely from the wste. Previous work hs shown tht 4-methyl-phenol (likely m/z 109) is directly excreted s fermenttion product of the protein tyrosine, but it cn lso be emitted fter lter trnsformtion within the wste (16, 17). The fluxes of ROGs, methnol, nd cetic cid from the lctting cows plus wste were sttisticlly lrger thn the corresponding fluxes from wste lone. The wste fluxes were in turn lrger thn those from the empty chmber (Tbles 2 nd 3). This implies these VOCs were primrily derived from cows, nd emitted in comprtively smll quntities from the wste. This once gin ssumes the wste only fluxes re representtive of those from the previous dy. In contrst there ws no such difference for dry cows (Tble 3), implying the entirety of these VOC emissions were derived from the wste lone. The verge TOG fluxes from the wstes of ll dry nd ll lctting cows were 12 nd 18 µg cow -1 s -1, respectively, nd were dominted by ROGs (74 nd 77%). Dily VOC Ptterns. Figure 2 shows dily ptterns of methnol, DMS, nd cetone + propnl fluxes from dry cows nd their wste. All fluxes incresed immeditely fter cows entered the chmber nd on subsequent mornings fter clening. Methnol nd DMS fluxes were highest initilly then decresed, while cetone + propnl remined comprtively constnt. Once the cows were removed, methnol fluxes continued while the others cesed. Methnol nd DMS cn be creted during rumen fermenttion of the feed. Methnol derives from crbohydrte nd proteins, while DMS derives from the mino cid cysteine (16). DMS fluxes re known to pek severl hours fter feeding (8, 13), implying our dry cows fed t chmber entry. Acetone is relesed in the lungs of mny living orgnisms s result of metbolic ft burning nd ws thus detected whenever the cows were present. Despite the fct Figure 2 shows tht lrger DMS nd methnol fluxes occurred from dry cows plus wste s compred to wste lone, the rnge of fluxes when cows were present ws so lrge tht these pprent differences were not sttisticlly significnt (Tble 3). Interprettion of the emissions sources my be confounded by time, s the wste ws excreted 1 dy before it ws smpled lone. The sttistics previously discussed implied the cows lone were responsible for most of the emissions of severl compounds. However, it is possible those emissions were in prt due to the wste, if they were emitted with high initil flux tht decresed over the 2 dy enclosure. It is much more likely this occurred for compounds which did not hve cler flux decreses when the cows exited the chmber (i.e., methnol, m/z 109) thn for compounds which did (i.e., CO 2,CH 4, DMS, cetone + propnl; Figures 1 nd 2). Longer enclosure periods could result in very different VOC emissions ptterns. For exmple, it cn often tke month or more in liquid mnure storge lgoons to see lrge VOC increses (18). Therefore, while the reported fluxes from dy-old wste cn be compred to those mesured when cows were present, they re likely inccurte for wste stored longer thn severl dys. SLC Affects Fluxes. Dry cows undergo significnt trnsition s they prepre for clving. Tht ws exhibited by lrger CO 2, ROG, nd some individul VOC fluxes (e.g., methnol) for close up cows plus wste thn for fr off cows plus wste. These differences could be due to incresed feed consumption, chnges in diet composition, or chnges in cow physiology, but it ws not possible to deconvolute these fctors. Previous work hs shown tht incresing the mount of dietry protein provided to close up cows resulted in incresed urinry phenols (16, 17). The verge m/z 109 (likely 4-methyl-phenol) fluxes from the wste of close up cows reported here were lrger thn those from ll other wstes. If lctting cow does not et sufficient feed to sustin milk production, she undergoes ketosis (i.e., metbolizes excessive mounts of body ft to produce energy). This results in incresed production of ketones, including cetone, nd is most common in erly lcttion phse. Erly lcttion cows plus wste in this study hd the lrgest verge cetone + propnl fluxes. Isoprene ws included in the sttisticl nlysis s n exmple of VOC whose emissions from mmmls re typiclly correlted with generl metbolic rtes (5). Dry cows plus wste emitted significntly less isoprene thn lctting cows plus wste (Tble 3 nd unpublished dt). Acetic cid fluxes were lso significntly lrger for lctting thn dry cows plus wste. This ws likely due to the lrger mount of nonfibrous crbohydrtes present in their feed, which re typiclly fermented fster nd more completely thn the forge fed to dry cows. The lrgest compound fluxes observed were generlly emitted from either close up or lctting cows plus wste. VOL. xx, NO. xx, xxxx / ENVIRON. 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6 TABLE 4. Normlized Ozone Formtion Potentil (OFP) for ROGs Emitted from Diry Cows in Mid Lcttion Phse VOC OFP fluxes (µg cow -1 s -1 ) isoprene 1.26 ( ( 0.08 m-xylene 1.09 ( ( 0.8 ethene 1.00 ( 0 NA formldehyde 0.60 ( 0.17 NA cetldehyde 0.50 ( ( 0.19 toluene 0.45 ( ( 0.45 ethnol 0.34 ( 0.07 g methnol flux m109 (4-methyl-phenol) ( 0.36 propionic cid ( 0.25 methnol 0.11 ( ( 4.8 cetic cid ( 1.3 Fluxes not significntly different from 0. Additionlly, compounds whose fluxes were sttisticlly lrger for the cows plus wste thn for the wste lone were more numerous for lctting thn for dry cows. An verge flux would clerly be insufficient to represent ll SLC, despite the fct ll experiments were performed with the sme breed nd physicl fctors tht cn ffect emission. Therefore we recommend tht future studies group cows by their SLC. O 3 Formtion Potentil of Diry Cow ROGs. Determining the effects of diry emissions on ir qulity requires including not just the fluxes but lso the O 3 formtion potentil (OFP) of ech individul ROG into n tmospheric model simultion. The OFP itself is lso defined through modeling s the mount of O 3 produced s result of dding smll mount of n individul ROG to n initil emissions mix, divided by the mount of ROG dded. Modeling ws beyond the scope of this work, but it ws possible to qulittively ssess the impct of diry ROG emissions on O 3 formtion in regions with significnt nthropogenic ir pollution. We normlized the results of three independent OFP clcultions (19-21) for ll ROGs for which OFP were vilble to those of ethene nd verged them (Tble 4). The ROGs we observed with the highest fluxes, ethnol nd methnol, hd OFPs 33 or 10% those of typicl combustion (ethene) or biogenic (isoprene) ROGs. The ROGs with highest OFPs hd fluxes tht often were not significntly different from 0. We qulittively conclude tht diry cows hve much smller impct on ozone formtion per VOC mss emitted thn combustion or biogenic sources. The ROG emitted s percent of TOG when cows were present in the chmber ws 0.8 ( 0.2%. Including rough estimte of the ethnol flux () methnol flux) brings this to 1.3%. This is fctor of 6-10 lower thn the 8% historiclly used by Cliforni regultory gencies for development of cow ROG emission inventories (4). The PTR-MS does not mesure lknes nd lkenes, but lrge fluxes re not expected (10). Additionlly, their OFPs re similr to, or less thn, tht of ethene (19-21). We do not report quntittive dt for formldehyde nd methylmines. VFAs >C 4, nd lrge moleculr weight phenols, sulfur, nd nitrogenous compound fluxes my be lower limits. Except for formldehyde, OFP re not vilble for these compounds s their photochemistry hs not been thought to produce lrge mounts of O 3. Even if we re only cpturing third of the ROG emissions, which we believe is considerble underestimte bsed on reltive emission fluxes from other published work (i.e., 8-10, 13), ROG would still be only third of the 8% estimte. Our mjor findings, tht (1) the OFP of ROGs emitted by diry cows re frction of those for typicl combustion or biogenic ROGs nd (2) tht the ROG/TOG rtio mesured ws fctor of 6-10 lower thn tht used historiclly, suggest tht ROG emissions from diry cows provide much smller contribution to O 3 formtion thn currently estimted for regultory purposes in Cliforni. Acknowledgments Funding ws provided by EPA Region IX, the Cliforni Diry Reserch Foundtion, nd the UC Agriculturl Experimentl Sttion. We grtefully cknowledge Los Gtos Reserch, Inc. for the use of their cvity-enhnced-bsorption spectrometer nd D. Ledgerwood nd R. Monteiro for ssistnce with the cows. Supporting Informtion Avilble PTR-MS ccurcy nd precision re presented. This mteril is vilble free of chrge vi the Internet t pubs.cs.org. Literture Cited (1) Schwehr, B. Definitions of VOC nd ROG. Cliforni Air Resources Bord, Plnning nd Technicl Support Division, Emission Inventory Brnch: Scrmento, CA, (2) Sn Joquin Vlley Air Pollution Control District. 1-hour extreme ozone ttinment demonstrtion pln (3) Ritzmn, E. G.; Benedict, F. G. Nutritionl physiology of the dult ruminnt; Crnegie Institute: Wshington, DC, (4) U.S. Environmentl Protection Agency. Voltile Orgnic Compound (VOC) Species Dt Mnul, Second Edition; EPA-450/ ; July (5) Lindinger, W.; Hnsel, A.; Jordn, A. On-line monitoring of voltile orgnic compounds t pptv levels by mens of Proton- Trnsfer-Rection Mss Spectrometry (PTR-MS): Medicl pplictions, food control, nd environmentl reserch. Int. J. Mss. Spec. Ion. Proc. 1998, 173, (6) Ochii, N.; Tsuji, A.; Nkmur, N.; Dishim, S.; Crdin, D. B. 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P.; Gupt, M.; O Keefe, A. Sensitive bsorption mesurements in the ner-infred region using off-xis integrted-cvity-output spectroscopy. Appl. Phys. B. 2002, 75, (12) Wilkerson, V. A.; Csper, D. P.; Mertens, D. R. The prediction of methne production of Holstein cows by severl equtions. J. Diry Sci. 1995, 78, (13) Willims, J.; Wng, N. Y.; Cicerone, R. J.; Ygi, K.; Kurihr, M.; Terd, F. Atmospheric methyl hlides nd dimethylsulfide from cttle. Globl Biogeochem. Cyc. 1999, 13 (2) (14) Kinsmn, R.; Suer, F. D.; Jckson, H. A.; Wolynetz, M. S. Methne nd crbon dioxide emissions from diry cows in full lcttion monitored over six-month period. J. Diry Sci. 1995, 78, (15) Fenske, J. D.; Pulson, S. E. Humn breth emissions of VOCs. J. Air Wste Mnge. Assoc. 1999, 49, (16) Mckie R. I.; Stroot, P. G.; Vrel, V. H. Biochemicl identifiction nd biologicl origin of key odor components in livestock wste. J. Anim. Sci , (17) Willig, S.; Losel, D.; Clus, R. Effects of resistnt potto strch on odor emission from feces in swine production units. J. Agric. Food Chem. 2005, 53, (18) Zhng, R. H.; M, Y.; Mitloehner, F.; McGrvey, J. Reducing Gs Emissions from Mnure Storges by Anerobic Digestion nd F 9 ENVIRON. SCI. & TECHNOL. / VOL. xx, NO. xx, xxxx

7 Aertion Technologies. Pper presented t ASAE Annul Interntionl Meeting, Tmp, FL, July 17-20, (19) Russell, A.; Milford, J.; Bergin, M. S.; McBride, S.; McNir, L.; Yng, Y.; Stockwell, W. R. T.; Croes, B. Urbn ozone control nd tmospheric rectivity of orgnic gses. Science 1995, 269, (20) Derwent, R. G.; Jenkin, M. E.; Sunders, S. A.; Pilling, M. J. Photochemicl ozone cretion potentils for orgnic compounds in Northwest Europe clculted with mster chemicl mechnism. Atmos. Environ. 1998, 32 (14), (21) Hkmi, A.; Hrley, R. A.; Milford, J. B.; Odmn, M. T.; Russell, A. G. Regionl, 3-dimensionl ssessment of the ozone forming potentil of orgnic compounds. Atmos. Environ. 2004, 38, Received for review June 20, Revised mnuscript received November 18, Accepted November 22, ES061475E PAGE EST: 6.1 VOL. xx, NO. xx, xxxx / ENVIRON. SCI. & TECHNOL. 9 G