Investigation Of HONO And NO_x Formation By Photochemical Reaction Of Nitrates | Posted on:2022-07-25 | Degree:Master | Type:Thesis | Country:China | Candidate:W W Xu | Full Text:PDF | GTID:2531306935455424 | Subject:Environmental Science | Abstract/Summary: | PDF Full Text Request | Nitrates are one of the main components in atmospheric aerosols,and they have significant environmental and health effects.Nitrous acid(HONO)and nitrogen oxides(NOx,i.e.,NO and NO2)can be generated by the photolysis of nitrates.HONO photolysis is an important source of hydroxyl radical(HO·)in the atmosphere environment.Hydroxyl radicals can participate in the atmospheric oxidation cycles and react with most pollutants.Therefore,the photolysis of nitrates have important scientific significance for atmospheric chemistry.And related studies have shown that some mineral oxides and organic substances can promote the photolysis of nitrates.In this study,TiO2 and syringic acid were used as representative substances of mineral oxides and methoxy phenols,respectively.The effects of TiO2 or syringic acid on the formation of HONO and NOx from the nitrates photolysis were studied using a cylindrical-shape reactor coupled to a NOx analyzer.The changes in the compositions of nitrates after the photolysis were analyzed by the in situ diffuse reflectance infrared spectrometer(In situ DRIFTS).The optical properties of TiO2 and methoxy phenols were analyzed using ultraviolet-visible spectrophotometer(UV-vis).The specific results of this study are obtained as follows:The photochemical reaction between TiO2 and nitrates shows that TiO2 played important roles in the emission flux density of NO2(RNO2)and HONO(RHONO),depending on crystal structures and mass fractions of TiO2.RNO2 and RHONO significantly decreased with increasing the rutile and anatase mass fractions from 0%to 8%and 0.5%,respectively.Nevertheless,with further increasing the anatase mass fractions to 8%,there was an increase in RNO2 and RHONO.RNO2 had positive correlation with the KNO3 mass(1%~20%),irradiation intensity(80~400 W/m2)and temperature(278~308 K).RNO2 had the maximum value at the relative humidity(RH)of 55%.RHONO slightly varied with the KNO3 mass and temperature,whereas it increased with the irradiation intensity and RH.In addition,the mechanism and atmospheric implications for NO2 and HONO emissions from the photochemical reaction of nitrates with TiO2 were discussed.The photochemical reaction between methoxy phenols and nitrates shows that the HONO and NO emissions from the nitrates photolysis were significantly promoted in the presence of syringic acid.The emission flux density of HONO(RHONO)increased with the mass ratio of syringic acid to nitrates(1.6×10-5~1.6 1×10-3)and irradiation intensity(36~267 W/m2),and it had the maximum value at the relative humidity(RH)of 40%and the temperature of 298 K.The emission flux density of NO(RNO)increased with increasing the mass ratio of syringic acid to nitrates and irradiation intensity,whereas it had small changes with the RH and temperature.The in situ DRIFTS results confirm that the absorption peak intensity of nitrate(NO3-)decreased continuously with the increase of irradiation time until the equilibrium state was finally reached.Moreover,pseudo first order dynamics study demonstrates that syringic acid could accelerate the photolysis of nitrates.Finally,the mechanism and atmospheric significance for HONO and NO emissions from the photochemical reaction of nitrates with syring acid were discussed. | Keywords/Search Tags: | nitrates, TiO2, syringic acid, photolysis, HONO, NO_x | PDF Full Text Request | Related items |
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