Fotodisociacija dušikovih oksidov v troposferi

• Main Author: Gregori, Erik
• Other Authors: Kalčikova, Gabriela
• Format: Bachelor Thesis
• Language: Slovenian
• Published: 2019
• Subjects: atmosfera; dušikovi oksidi; fotokemija; kvantna kemija; metode gostotnih funkcionalov; atmosphere; density functional theory; nitrogen oxides; photochemistry; quantum chemistry; sami
• Online Access: https://repozitorij.uni-lj.si/IzpisGradiva.php?id=109951; https://repozitorij.uni-lj.si/Dokument.php?id=121557&dn=; https://plus.si.cobiss.net/opac7/bib/1538421955?lang=sl

Dušikovi oksidi imajo v troposferi pomembno vlogo na okoliški zrak. Sodelujejo pri nastanku kislega dežja, posredno učinkujejo predvsem na dihala organizmov in so edini poznan vir tvorbe večjih količin troposferskega ozona. Izkazalo se je, da se njihova koncentracija v troposferi v letih narašča in je posledica antropogenega delovanja. Večji del dušikovih oksidov se v troposferi akumulira pri gorenju fosilnih goriv, sežigu biomase ter kot posledica intenzivnega gojenja. Poleg tega, da so že sami nevarni za organizme, so v troposferi fotoaktivni. Z absorpcijo fotona ustrezne valovne dolžine, ki prihaja iz vpadne svetlobe Sonca, potečereakcija fotodisociacije. Pri tem nastane med drugim zelo reaktiven atomarni kisik, ki skoraj v trenutku reagira z molekulo O2 prisotno v okolici. S to reakcijo nastaja troposferski ozon, ki je ena najpomembnejših komponent fotokemičnega smoga. Fotokemijski procesi potekajo v vzbujenih stanjihin so izredno kompleksne narave,saj vključujejo poleg fizikalnih pojavov še nekatere kvantne pojave, kot je naprimer trk fotona z molekulo. Hitrost reakcije tako pogojuje več parametrov, pomembnejšo vlogo pa imajo pritem Sončni zenitni kot, absorpcijski presek in kvantni izkoristek. S pomočjo programske opreme Gaussian smo opravili osnovno termodinamsko analizo reakcije, ki lahko služi kot začetek za nadaljne raziskave reakcijskega mehanizma in kinetike reakcije. Pridobljene podatke smo ovrednotili preko pridobljenega teoretičnega znanja in preko primerjave z dostopnimi eksperimentalnimi podatki iz literature. Nitrogen oxides play a key role in the pollution of the troposphere. They participate in processes that involve the formation of the acid rain and tropospheric ozone and they directly impact the biota. An increment of their concentration has been observed through the years as a consequence of anthropogenic activity. Their accumulation in the troposphere is mostly attributed to the burning of fossil fuels, burning of biomasses and intense growing methods. Further the nitrogen oxides are a photoactive tropospheric species. They photodissociate after absorbing a photon with the appropriate wave length from the incoming solar radiation. One of the products of this reaction is atomic oxygen which instantelly reacts with the O2 molecule in the surroundings. This reaction leads to the formation of tropospheric ozone, one of the keycomponents of the photochemical smog. The photochemical processes occur in excited states and, beside various physical phenomena, some quantum phenomena, such as the collision of a photon and a molecule, are involved. Hence,there action rate depends on various parameters, primarily the solar zenith angle,the absorption cross-section and the quantum yield. With the use of the Gaussian software we did a basic thermodynamic analysis of the reaction which can be used as a beginning for further research of the reaction mechanism and reaction kinetics. We evaluated the obtained data from the acquired theoretical knowledge and through a comparison with the available experimental data.