Catalogo Articoli (Spogli Riviste)

OPAC HELP

Titolo:
PHOTOCHEMICAL MODELING OF HYDROXYL AND ITS RELATIONSHIP TO OTHER SPECIES DURING THE TROPOSPHERIC OH PHOTOCHEMISTRY EXPERIMENT
Autore:
MCKEEN SA; MOUNT G; EISELE F; WILLIAMS E; HARDER J; GOLDAN P; KUSTER W; LIU SC; BAUMANN K; TANNER D; FRIED A; SEWELL S; CANTRELL C; SHETTER R;
Indirizzi:
NOAA,AERON LAB,R-E-AL4,325 BROADWAY BOULDER CO 80303 UNIV COLORADO,COOPERAT INST RES ENVIRONM SCI BOULDER CO 80309 NATL CTR ATMOSPHER RES BOULDER CO 80303
Titolo Testata:
JOURNAL OF GEOPHYSICAL RESEARCH-ATMOSPHERES
fascicolo: D5, volume: 102, anno: 1997,
pagine: 6467 - 6493
Fonte:
ISI
Lingua:
ENG
Soggetto:
METHYL VINYL KETONE; GAS-PHASE REACTIONS; CHEMICAL MECHANISM; UNITED-STATES; NIWOT-RIDGE; PHOTOSTATIONARY STATE; NATURAL HYDROCARBONS; ORGANIC-COMPOUNDS; PEROXY-RADICALS; ALPHA-PINENE;
Tipo documento:
Article
Natura:
Periodico
Settore Disciplinare:
Science Citation Index Expanded
Citazioni:
49
Recensione:
Indirizzi per estratti:
Citazione:
S.A. Mckeen et al., "PHOTOCHEMICAL MODELING OF HYDROXYL AND ITS RELATIONSHIP TO OTHER SPECIES DURING THE TROPOSPHERIC OH PHOTOCHEMISTRY EXPERIMENT", JOURNAL OF GEOPHYSICAL RESEARCH-ATMOSPHERES, 102(D5), 1997, pp. 6467-6493

Abstract

Because of the extremely short photochemical lifetime of troposphericOH, comparisons between observation and model calculations should be an effective test of our understanding of the photochemical processes controlling the concentration of OH, the primary oxidant in the atmosphere. However, unambiguous estimates of calculated OH require sufficiently accurate and complete measurements of the key species and physical variables that determine OH concentrations. The Tropospheric OH Photochemistry Experiment (TOHPE) provides an extremely complete set of measurements, sometimes from multiple independent experimental platforms, that allows such a test to be conducted. When the calculations explicitly use observed NO, NO2, hydrocarbons, and formaldehyde, the photochemical model consistently overpredicts in situ observed OH by similarto 50% for the relatively clean conditions predominantly encountered at Idaho Hill. The model bias is much higher when only CH4-CO chemistry is assumed, or NO is calculated from the steady state assumption. For the most polluted conditions encountered during the campaign, the model results and observations show better agreement. Although the comparison between calculated and observed OH can be considered reasonably good given the +/-30% uncertainties of the OH instruments and various uncertainties in the model, the consistent bias suggests a fundamentaldifference between theoretical expectations and the measurements. Several explanations for this discrepancy are possible, including errors in the measurements, unidentified hydrocarbons, losses of HOx to aerosols and the Earth's surface, and unexpected peroxy radical chemistry. Assuming a single unidentified type of hydrocarbon is responsible, theamount of additional hydrocarbon needed to reduce theoretical OH to observed levels is a factor of 2 to 3 greater than the OH-reactivity-weighted hydrocarbon content measured at the site. Constraints can be placed on the production and yield of various radicals formed in the oxidation sequence by considering the observed levels of certain key oxidation products such as formaldehyde and acetaldehyde. The model results imply that, under midday clean westerly flow conditions, formaldehyde levels are fairly consistent with the OH and hydrocarbon observations, but observed acetaldehyde levels are a factor of 4 larger than whatis expected and also imply a biogenic source. Levels of methacrolein and methylvinylketone are much lower than expected from steady state isoprene chemistry, which implies important removal mechanisms or missing information regarding the kinetics of isoprene oxidation within themodel. In a prognostic model application, additional hydrocarbons areadded to the model in order to force calculated OH to observed levels. Although the products and oxidation steps related to pinenes and other biogenic hydrocarbons are somewhat uncertain, the addition of a species with an oxidation mechanism similar to that expected from C-10 pinenes would be consistent with the complete set of observations, as opposed to naturally emitted isoprene or any of the anthropogenic hydrocarbons examined in the model. Further constraints on the abundance of peroxy radicals are necessary in order to fill the gaps in our understanding of OH photochemistry for the clean continental conditions typical of Idaho Hill.

ASDD Area Sistemi Dipartimentali e Documentali, Università di Bologna, Catalogo delle riviste ed altri periodici
Documento generato il 29/03/20 alle ore 17:52:07