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Titolo:
ISOPRENE FLUXES MEASURED BY ENCLOSURE, RELAXED EDDY ACCUMULATION, SURFACE-LAYER GRADIENT, MIXED-LAYER GRADIENT, AND MIXED-LAYER MASS-BALANCE TECHNIQUES
Autore:
GUENTHER A; BAUGH W; DAVIS K; HAMPTON G; HARLEY P; KLINGER L; VIERLING L; ZIMMERMAN P; ALLWINE E; DILTS S; LAMB B; WESTBERG H; BALDOCCHI D; GERON C; PIERCE T;
Indirizzi:
NATL CTR ATMOSPHER RES,DIV ATMOSPHER CHEM,POB 3000 BOULDER CO 80307 WASHINGTON STATE UNIV,DEPT CIVIL & ENVIRONM ENGN PULLMAN WA 99164 NOAA,DIV ATMOSPHER TURBULENCE & DIFFUS OAK RIDGE TN 37830 US EPA,OFF RES & DEV RES TRIANGLE PK NC 27711
Titolo Testata:
JOURNAL OF GEOPHYSICAL RESEARCH-ATMOSPHERES
fascicolo: D13, volume: 101, anno: 1996,
pagine: 18555 - 18567
Fonte:
ISI
Lingua:
ENG
Soggetto:
UNITED-STATES; ORGANIC-COMPOUNDS; WATER-VAPOR; EMISSIONS; MODEL; INVENTORY; FOREST; HEAT;
Tipo documento:
Article
Natura:
Periodico
Settore Disciplinare:
Science Citation Index Expanded
Citazioni:
22
Recensione:
Indirizzi per estratti:
Citazione:
A. Guenther et al., "ISOPRENE FLUXES MEASURED BY ENCLOSURE, RELAXED EDDY ACCUMULATION, SURFACE-LAYER GRADIENT, MIXED-LAYER GRADIENT, AND MIXED-LAYER MASS-BALANCE TECHNIQUES", JOURNAL OF GEOPHYSICAL RESEARCH-ATMOSPHERES, 101(D13), 1996, pp. 18555-18567

Abstract

Isoprene fluxes were estimated using eight different measurement techniques at a forested site near Oak Ridge, Tennessee, during July and August 1992. Fluxes from individual leaves and entire branches were estimated with four enclosure systems, including one system that controlsleaf temperature and light. Variations in isoprene emission with changes in light, temperature, and canopy depth were investigated with leaf enclosure measurements. Representative emission rates for the dominant vegetation in the region were determined with branch enclosure measurements. Species from six tree genera had negligible Isoprene emissions, while significant emissions were observed for Quercus, Liquidambar, and Nyssa species. Above-canopy isoprene fluxes were estimated with surface layer gradients and relaxed eddy accumulation measurements from a 44-m tower. Midday net emission fluxes from the canopy were typically 3 to 5 mg C m(-2) h(-1), although net isoprene deposition fluxes of -0.2 to 2 mg C m(-2) h(-1) were occasionally observed in early morning and late afternoon. Above-canopy CO2 fluxes estimated by eddy correlation using either an open path sensor or a closed path sensor agreedwithin +/-5%. Relaxed eddy accumulation estimates of CO2 fluxes were within 15% of the eddy correlation estimates. Daytime isoprene mixing ratios in the mixed layer were investigated with a tethered balloon sampling system and ranged from 0.2 to 5 ppbv, averaging 0.8 ppbv. The isoprene mixing ratios in the mixed layer above the forested landscape were used to estimate isoprene fluxes of 2 to 8 mg C m(-2) h(-1) with mixed layer gradient and mixed layer mass balance techniques. Total foliar density and dominant tree species composition for an approximately 8100 km(2) region were estimated using high-resolution (30 m) satellite data with classifications supervised by ground measurements. A biogenic isoprene emission model used to compare flux measurements, ranging from leaf scale (10 cm(2)) to landscape scale (10(2) km(2)), indicated agreement to within +/-25%, the uncertainty associated with these measurement techniques. Existing biogenic emission models use isopreneemission rate capacities that range from 14.7 to 70 mu g C g(-1) h(-1) (leaf temperature of 30 degrees C and photosynthetically active radiation of 1000 mu mol m(-2) s(-1)) for oak foliage. An isoprene emission rate capacity of 100 mu g C g(-1) h(-1) for oaks in this region is more realistic and is recommended, based on these measurements.

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Documento generato il 08/07/20 alle ore 06:41:24