Nitrate Photochemistry in NaY Zeolite: Product Formation and Product Stability under Different Environmental Conditions

Abstract

In the atmosphere, mineral dust particles are often associated with adsorbed nitrate from heterogeneous reactions with nitrogen oxides (N2O5, HNO3, NO3, and NO2). Nitrate ions associated with mineral dust particles can undergo further reactions including those initiated by solar radiation. Although nitrate photochemistry in aqueous media is fairly well studied, much less is known about the photochemistry of nitrate adsorbed on mineral dust particles. In this study, the photochemistry of nitrate from HNO3 adsorption in NaY zeolite under different environmental conditions has been investigated using transmission FTIR spectroscopy. NaY zeolite is used as a model zeolite for studying reactions that can occur in confined space such as those found in porous materials including naturally occurring zeolites and clays. Upon nitrate photolysis under dry conditions (relative humidity, RH, < 1%), surface nitrite is formed as the major adsorbed product. Although nitrite has been proposed as a product in the photochemistry of nitrate adsorbed on metal oxide particle surfaces, such as on alumina, it has not been previously detected. The stability of adsorbed nitrite in NaY is attributed to the confined three-dimensional structure of the porous zeolite, which contains a charge compensating cation that can stabilize the nitrite ion product. Besides adsorbed nitrite, small amounts of gas phase nitrogen-containing products are observed as well including NO2, NO, and N2O at long irradiation times. The amount of nitrite formed via nitrate photochemistry decreases with increasing relative humidity, whereas gas phase NO and N2O become the only detectable products. Gas-phase NO2 does not observe at RH > 1%. In the presence of gas phase ammonia, ammonium nitrate is formed in NaY zeolite. Photochemistry of ammonium nitrate yields gas phase N2O as the sole gas phase product. Evidence for an NH2 intermediate in the formation of N2O is identified with FTIR spectroscopy for HNO3 adsorption and photochemistry in NH4Y zeolite. Here, we discuss mechanisms for the formation of these intermediates from nitrate photochemistry as well as possible atmospheric implications.

Chemical characterization of fine particulate matter emitted by peat fires in Central Kalimantan, Indonesia, during the 2015 El Niño

“…The molar concentrations of gaseous NH 3 and NO + HONO were 33 times and 312 times higher than that of NH + 4 and NO − 3 , respectively, consistent with a dominance of gas-phase precursors in fresh peat-burning emissions (Stockwell et al, 2016). The atmospheric oxidation of NO and HONO could increase the concentration of NO − 3 (Gankanda and Grassian, 2013;Gankanda et al, 2016), while acid-base reactions convert NH 3 to NH + 4 , thus leading to increased concentrations of these secondary inorganic products in aged peat smoke.…”

Chemical characterization of fine particulate matter emitted by peat fires in Central Kalimantan, Indonesia, during the 2015 El Niño

“…The molar concentration of 5 gaseous NH 3 and NO+HONO were 33 times and 312 times higher than that of NH 4 + and NO 3 -, respectively consistent with a dominance of gas phase precursors in fresh peat burning emissions (Stockwell et al, 2016). The atmospheric oxidation of NO and HONO could increase the concentration of NO 3 - (Gankanda and Grassian, 2013;Gankanda et al, 2016), while acid base reactions convert NH 3 to NH 4 + , thus leading to increased concentrations of these secondary inorganic products in aged peat 10 smoke.…”

Chemical characterization of biomass burning and sea spray aerosol

“…During long range transport, the aerosol particles encounter different atmospheric gases, moisture and sunlight, and undergo surface and multi-phase chemical reactions altering the chemical and physical properties of the primary aerosol particle. [7][8][9][10][11] Further, gas phase molecules can nucleate new particles or condense on to existing primary particles to form secondary aerosols via various chemical reactions affecting the composition of the atmospheric PM. [12][13][14][15][16][17] Further, both chemical composition of the particle and number of particles changes significantly during the different time of the year.…”