Photolytic processing of secondary organic aerosols dissolved in cloud droplets

The effect of UV irradiation on the molecular composition of aqueous extracts of secondary organic aerosol (SOA) was investigated. SOA was prepared by the dark reaction of ozone and d-limonene at 0.05-1 ppm precursor concentrations and collected with a particle-into-liquid sampler (PILS). The PILS extracts were photolyzed by 300-400 nm radiation for up to 24 h. Water-soluble SOA constituents were analyzed using high-resolution electrospray ionization mass spectrometry (HR-ESI-MS) at different stages of photolysis for all SOA precursor concentrations. Exposure to UV radiation increased the average O/C ratio and decreased the average double bond equivalent (DBE) of the dissolved SOA compounds. Oligomeric compounds were significantly decreased by photolysis relative to the monomeric compounds. Direct pH measurements showed that acidic compounds increased in abundance upon photolysis. Methanol reactivity analysis revealed significant photodissociation of molecules containing carbonyl groups and the formation of carboxylic acids. Aldehydes, such as limononaldehyde, were almost completely removed. The removal of carbonyls was further confirmed by the UV/Vis absorption spectroscopy of the SOA extracts where the absorbance in the carbonyl n→π* band decreased significantly upon photolysis. The effective quantum yield (the number of carbonyls destroyed per photon absorbed) was estimated as ～0.03. The total concentration of peroxides did not change significantly during photolysis as quantified with an iodometric test. Although organic peroxides were photolyzed, the likely end products of photolysis were smaller peroxides, including hydrogen peroxide, resulting in a no net change in the peroxide content. Photolysis of dry limonene SOA deposited on substrates was investigated in a separate set of experiments. The observed effects on the average O/C and DBE were similar to the aqueous photolysis, but the extent of chemical change was smaller in dry SOA. Our results suggest that biogenic SOA dissolved in cloud and fog droplets will undergo significant photolytic processing on a time scale of hours to days. This type of photolytic processing may account for the discrepancy between the higher values of O/C measured in the field experiments relative to the laboratory measurements on SOA in smog chambers. In addition, the direct photolysis of oligomeric compounds may be responsible for the scarcity of their observation in the field.     

Secondary organic aerosol formation during the photooxidation of toluene: NOx dependence of chemical composition

The photooxidation of toluene is a potential source of secondary organic aerosol (SOA) in urban air, but only a small portion of the compounds present in SOA have been identified. In this study, we analyzed the chemical compositions of SOA produced by photoirradiation of the toluene/NOx/air system in laboratory chamber experiments by a combination of liquid chromatography-mass spectrometry, hybrid high-performance liquid chromatography-mass spectrometry, and iodometry-spectrophotometry. The dependence of the chemical composition on the initial NOx concentration was examined at initial NO concentrations ([NO]0) of 0.2 and 1 ppmv. Fifteen semivolatile products, including aromatic and ring-cleavage compounds, were quantified. However, the quantified products comprised only a small portion ( approximately 1 wt %) of the total aerosol mass. The total SOA yield ( approximately 13 wt %), the ratio of organic peroxides to total SOA mass ( approximately 17 wt %), and the density of SOA ( approximately 1.4 g cm-3) were independent of the NOx level, suggesting that the reaction mechanisms of the formation of major SOA products at [NO]0 = 0.2 and 1 ppmv are essentially the same. The negative-ion mass spectra of SOA samples showed that ion signals attributed to hemiacetal oligomers and/or decomposition products of peroxy hemiacetal oligomers were detected in the range of mass-to-charge ratios (m/z) between 200 and 500. The highest signals were detected at m/z = 155 and 177, and these were tentatively assigned to C7 unsaturated oxacyclic oxocarboxylic acids and C7 unsaturated oxacyclic dicarboxylic acids, respectively. We conclude that the major chemical components of the aerosol are hemiacetal and peroxy hemiacetal oligomers and low-molecular-weight dicarboxylic acids.     

Low‐Molecular Weight and Oligomeric Components in Secondary Organic Aerosol from the Photooxidation of p‐Xylene

A laboratory study was performed to investigate the composition of secondary organic aerosol (SOA) products from photooxidation of the aromatic hydrocarbon p‐xylene. The experiments were conducted by irradiating p‐xylene/CH₃ONO/NO/air mixtures in a home‐made smog chamber. The aerosol time‐of‐flight mass spectrometer (ATOFMS) was used to measure the size and the chemical composition of individual secondary organic aerosol particles in real‐time. According to a large number of single aerosol diameters and mass spectra, the size distribution and chemical composition of SOA were determined statistically. Experimental results showed that aerosol created by p‐xylene photooxidation is predominantly in the form of fine particles, which have diameters less than 2.5 μm (i.e. PM2.5), and aromatic aldehyde, unsaturated dicarbonys, hydroxyl dicarbonys, and organic acid are major product components in the SOA after 2 hours photooxidation. After aging for more than 8 hours, about 10% of the particle mass consists of oligomers with a molecular mass up to 600 daltons. The possible reaction mechanisms leading to these products are also proposed.     

Chemical composition of secondary organic aerosol formed from the photooxidation of isoprene

Recent work in our laboratory has shown that the photooxidation of isoprene (2-methyl-1,3-butadiene, C(5)H(8)) leads to the formation of secondary organic aerosol (SOA). In the current study, the chemical composition of SOA from the photooxidation of isoprene over the full range of NO(x) conditions is investigated through a series of controlled laboratory chamber experiments. SOA composition is studied using a wide range of experimental techniques: electrospray ionization-mass spectrometry, matrix-assisted laser desorption ionization-mass spectrometry, high-resolution mass spectrometry, online aerosol mass spectrometry, gas chromatography/mass spectrometry, and an iodometric-spectroscopic method. Oligomerization was observed to be an important SOA formation pathway in all cases; however, the nature of the oligomers depends strongly on the NO(x) level, with acidic products formed under high-NO(x) conditions only. We present, to our knowledge, the first evidence of particle-phase esterification reactions in SOA, where the further oxidation of the isoprene oxidation product methacrolein under high-NO(x) conditions produces polyesters involving 2-methylglyceric acid as a key monomeric unit. These oligomers comprise approximately 22-34% of the high-NO(x) SOA mass. Under low-NO(x) conditions, organic peroxides contribute significantly to the low-NO(x) SOA mass (approximately 61% when SOA forms by nucleation and approximately 25-30% in the presence of seed particles). The contribution of organic peroxides in the SOA decreases with time, indicating photochemical aging. Hemiacetal dimers are found to form from C(5) alkene triols and 2-methyltetrols under low-NO(x) conditions; these compounds are also found in aerosol collected from the Amazonian rainforest, demonstrating the atmospheric relevance of these low-NO(x) chamber experiments.     

Nitrate ion photochemistry at interfaces: a new mechanism for oxidation of alpha-pinene

The photooxidation of 0.6-0.9 ppm alpha-pinene in the presence of a deliquesced thin film of NaNO(3), and for comparison increasing concentrations of NO(2), was studied in a 100 L Teflon(R) chamber at relative humidities from 72-88% and temperatures from 296-304 K. The loss of alpha-pinene and the formation of gaseous products were followed with time using proton transfer mass spectrometry. The yields of gas phase products were smaller in the NaNO(3) experiments than in NO(2) experiments. In addition, pinonic acid, pinic acid, trans-sobrerol and other unidentified products were detected in the extracts of the wall washings only for the NaNO(3) photolysis. These data indicate enhanced loss of alpha-pinene at the NaNO(3) thin film during photolysis. Supporting the experimental results are molecular dynamics simulations which predict that alpha-pinene has an affinity for the surface of the deliquesced nitrate thin film, enhancing the opportunity for oxidation of the impinging organic gas during the nitrate photolysis. This new mechanism of oxidation of organics may be partially responsible for the correlation between nitrate and the organic component of particles observed in many field studies, and may also contribute to the missing source of SOA needed to reconcile model predictions and field measurements. In addition, photolysis of nitrate on surfaces in the boundary layer may lead to oxidation of co-adsorbed organics.     

On-line photo-derivatization with flow injection and liquid chromatography-atmospheric pressure electrospray mass spectrometry for the identification of indoles

The application of on-line photochemistry with flow injection (FI) and liquid chromatography (LC) in conjunction with atmospheric pressure electrospray mass spectrometry (LC-APESI-MS) for the identification of similar indole derivatives is reported here. The photo-transformation of the indole compounds is strongly affected by the substituent groups on the aromatic and heterocyclic rings. Upon photolysis for 2.5 min, the mass spectrum of tryptamine (Try) which has no OH substituent on the aromatic ring does not differ greatly from that obtained without photolysis. However, after photolysis of serotonin (Ser) which has one OH group on C5 of the aromatic ring, the mass spectrum indicates the formation of dimers and higher molecular weight ions. The fragmentation pattern of 5-hydroxytryptophol (Phol) without photolysis resembles that of Ser with a base peak of m/z 160. Upon photolysis using MeOH-H₂O (10/90), Phol is found to form a base peak at m/z 375 (100%) and a major peak at m/z 214 (66%) in addition to other ions with lower abundance. Melatonin (Mel) and tryptophan (Phan) upon photolysis are found to form high molecular weight ions with a relative low abundance. The mass spectrum of indole-3-acetic acid (Inaa) with on-line photolysis also shows different ions that are not formed without photolysis.     

Kinetics of N(2)O(5) hydrolysis on secondary organic aerosol and mixed ammonium bisulfate-secondary organic aerosol particles

The kinetics of the hydrolysis reaction of N(2)O(5) on secondary organic aerosol (SOA) produced through the ozonolysis of α-pinene and on mixed ammonium bisulfate-SOA particles was investigated using an entrained aerosol flow tube coupled to a chemical ionization mass spectrometer. We report room temperature uptake coefficients, γ, on ammonium bisulfate and SOA particles at 50% relative humidity of 1.5 × 10(-2) ± 1.5 × 10(-3) and 1.5 × 10(-4) ± 2 × 10(-5), respectively. For the mixed ammonium bisulfate-SOA particles, γ decreased from 2.6 × 10(-3) ± 4 × 10(-4) to 3.0 × 10(-4) ± 3 × 10(-5) as the SOA mass fraction increased from 9 to 79, indicating a strong suppression in γ with the addition of organic material. There is an order-of-magnitude reduction in the uptake coefficient with the smallest amount of SOA material present and smaller additional reductions with increasing aerosol organic content. This newly coated organic layer may either decrease the mass accommodation coefficient of N(2)O(5) onto the particle or hinder the dissolution and diffusion of N(2)O(5) into the remainder of the aerosol after it has been accommodated onto the surface. The former corresponds to a surface effect and the latter to bulk processes. The low value of the uptake coefficient on pure SOA particles will likely make N(2)O(5) hydrolysis insignificant on such an aerosol, but atmospheric chemistry models need to account for the role that organics may play in suppressing the kinetics of this reaction on mixed organic-inorganic particles.     

水中低浓度有机氮化物的光解研究和总氮量的测定

本文测定了23种有机含氮物。在强紫外光辐射下,应用4%K₂S₂O₈为氧化剂,经酸、碱两步光解,除N-N键形成游离氮外,其它键型氮均在25分钟内定量分解。实验中精简了KO₃的还原步骤。对天然水和污水的分析均有较好的效果。     

Photochemical aging of α-pinene secondary organic aerosol: effects of OH radical sources and photolysis

This study addresses photochemical aging of secondary organic aerosol (SOA) produced from α-pinene ozonolysis. The SOA is aged via hydroxyl radical (OH) reactions with first-generation vapors and UV photolysis. OH radicals are created through tetramethylethylene ozonolysis, HOOH photolysis, or HONO photolysis, sources that vary in OH concentration and the presence or absence of UV illumination. Aging strongly influences observed SOA mass concentrations, but the behavior is complex. In the dark or with high concentrations of OH, vapors are functionalized, lowering their volatility, resulting in an increase in OA by a factor of 2-3. However, with lower concentrations of OH under UV illumination SOA mass concentrations decrease over time. We attribute this decrease to evaporation driven by photolysis of the highly functionalized second-generation products. The photolysis rates are rapid, a few percent of the NO(2) photolysis frequency, and can thus be highly competitive with other aging mechanisms in the atmosphere.     

Application of matrix-assisted laser desorption/ionization time-of-flight mass spectrometry to insoluble glucose oligomers in decomposed cellulose

An analytical approach is described for the molecular weight characterization of glucose oligomers from cellulose which had been decomposed by hot-compressed water (HCW). Microcrystalline cellulose was decomposed to 18% of water insoluble fraction (WI) plus 82% of water soluble fraction (WS) by HCW (295 degrees C, 10 mL/min). The glucose oligomers in the WI were analyzed by pericullar anion exchange chromatography, and oligomers longer than pentamers were detected. These results were also confirmed by matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOFMS). Many peaks derived from glucose oligomers with molecular weights less than 4000 Da were detected in the spectra. Mass differences between peaks were 162 Da, as expected for polymers composed of glucose units. This appears to be the first report concerning molecular weight determination of water or organic solvent insoluble compounds like glucose oligomers from cellulose using MALDI-TOFMS.     

4-取代-2-氨基嘧啶衍生物的合成

含乙酰基的芳杂环类化合物分别与过量40%~50%的N,N-二甲基甲酰胺-二甲基缩醛（DMF-DMA）在回流温度下进行反应,得到相应的中间产物3-(二甲氨基)-1-（取代）-2-丙烯-1-酮,收率为71.2%~85.2%。 所得中间产物在乙醇介质中,在乙醇钠存在下与盐酸胍回流反应5～7 h,制备了14个4-取代-2-氨基嘧啶类化合物,收率达66.6%~86.1%,产物经核磁、质谱、元素分析等进行了表征。     

Identification of phototransformation products of sildenafil (Viagra) and its N‐demethylated human metabolite under simulated sunlight

Recent publications on pharmaceutical monitoring are increasingly covering the field of illicit drugs and lately the forensic evaluation of designing illegal analogs of lifestyle drugs like the phosphodiesterase type 5 (PDE‐5) inhibitors Viagra (sildenafil), Levitra (vardenafil) and Cialis (tadalafil). Recently, the presence of all three erectile dysfunction treatment drugs has been reported in wastewaters at very low concentrations. In the environment, contaminants undergo various physical or chemical processes classified into abiotic (photolysis, hydrolysis) and biotic (biodegradation) reactions. Thus, changes in the chemical structure lead to the formation of new transformation products, which may persist in the environment or be further degraded. This study describes the photolysis of sildenafil (SDF) and its human metabolite N‐demethylsildenafil (DM‐SDF) under simulated solar radiation (Xenon lamp). Following chromatographic separation of the irradiated samples, eight photoproducts in the SDF samples and six photoproducts for DM‐SDF were detected and characterized. The combination of ultra performance liquid chromatography‐electrospray ionization‐quadrupole time‐of‐flight‐mass spectrometry (UPLC‐ESI‐QToF‐MS), liquid chromatography‐atmospheric pressure chemical ionization‐triple quadrupole mass spectrometry (LC‐APCI‐QqQ‐MS) and hydrogen/deuterium‐exchange experiments allowed to propose plausible chemical structures for the photoproducts, taking into account the characteristic fragmentation patterns and the accurate mass measurements. These mass spectral data provided sound evidence for the susceptibility of the piperazine ring toward photodegradation. A gradual breakdown of this heterocyclic structure gave rise to a series of products, which in part were identical for SDF and DM‐SDF. The sulfonic acid, as the formal product of sulfonamide hydrolysis, was identified as key intermediate in the photolysis pathway. In both drug/metabolite molecules, phototransformation processes taking place beyond the sulfonamide group were deemed to be of minor relevance. Copyright © 2012 John Wiley & Sons, Ltd.     

Cobalt(III) complexes of unsaturated carboxylic acids: synthesis, characterization, and photochemical studies in aqueous medium

Cobalt(III) ammine complexes coordinated to carboxylic acids are classic examples showing photoredox reactions originating from the ligand to metal charge transfer excited states. Cobalt(III) pentaammine complexes coordinated to unsaturated carboxylic acids as ligands were synthesized and characterized by spectroscopic methods. The photolysis of these complexes produces a carboxylate free radical. This free radical undergoes further transformation to form organic photoproducts. The organic photoproducts were characterized by spectroscopic methods. The nature of the decomposition products from the organic photoproduct was examined in detail. The quantum yields were also determined. The photochemical reactions have the potential to produce novel compounds from the decarboxylation of unsaturated acids, which shows interesting reaction pathways.     

系列烯基化芳香杂环化合物的合成及结构表征

报道了一个简单、 高选择性合成烯基化芳香杂环化合物的反应体系. 在钯的催化作用下, 以乙酸/乙酸酐或四氢呋喃为溶剂, 芳香杂环化合物与烯基化试剂进行交叉脱氢偶联, 合成了系列具有潜在光学活性的烯基化芳香杂环化合物, 确定了最佳反应条件. 采用紫外光谱、 核磁共振氢谱和X射线单晶衍射对目标化合物进行了表征, 并对反应机理进行了探讨.     

Oligomer Formation Pathways in Secondary Organic Aerosol from MS and MS/MS Measurements with High Mass Accuracy and Resolving Power

Secondary organic aerosol (SOA) is formed when organic molecules react with oxidants in the gas phase to form particulate matter. Recent measurements have shown that more than half of the mass of laboratory-generated SOA consists of high molecular weight oligomeric compounds. In this work, the formation mechanisms of oligomers produced in the laboratory by ozonolysis of α-pinene, an important SOA precursor in ambient air, are studied by MS and MS/MS measurements with high accuracy and resolving power to characterize monomer building blocks and the reactions that couple them together. The distribution of oligomers in an SOA sample is complex, typically yielding over 1000 elemental formulas that can be assigned from an electrospray ionization mass spectrum. Despite this complexity, MS/MS spectra can be found that give strong evidence for specific oligomer formation pathways that have been postulated but not confirmed. These include aldol and gem-diol reactions of carbonyls as well as peroxyhemiacetal formation from hydroperoxides. The strongest evidence for carbonyl reactions is in the formation of hydrated products. Less compelling evidence is found for dehydrated products and secondary ozonide formation. The number of times that a monomer building block is observed as a fragmentation product in the MS/MS spectra is shown to be independent of the monomer vapor pressure, suggesting that oligomer formation is not driven by equilibrium partitioning of a monomer between the gas and particle phases, but rather by reactive uptake where a monomer collides with the particle surface and rapidly forms an oligomer.     

Contribution of carbonyl photochemistry to aging of atmospheric secondary organic aerosol

The photodegradation of secondary organic aerosol (SOA) material by actinic UV radiation was investigated. SOA was generated via the dark reaction of ozone and d-limonene, collected onto quartz-fiber filters, and exposed to wavelength-tunable radiation. Photochemical production of CO was monitored in situ by infrared cavity ring-down spectroscopy. A number of additional gas-phase products of SOA photodegradation were observed by gas chromatography, including methane, ethene, acetaldehyde, acetone, methanol, and 1-butene. The absorption spectrum of SOA material collected onto CaF2 windows was measured and compared with the photolysis action spectrum for the release of CO, a marker for Norrish type-I photocleavage of carbonyls. Both spectra had a band at approximately 300 nm corresponding to the overlapping n --> pi* transitions in nonconjugated carbonyls. The effective extinction coefficient of freshly prepared SOA was estimated to be on the order of 15 L mol(-1) cm(-1) at 300 nm, implying one carbonyl group in every SOA constituent. The absorption by the SOA material slowly increased in the visible and near-UV during storage of SOA in open air in the dark, presumably as a result of condensation reactions that increased the degree of conjugation in the SOA constituents. These observations suggest that photolysis of carbonyl functional groups represents a significant sink for monoterpene SOA compounds in the troposphere, with an estimated lifetime of several hours over the continental United States.     

Aqueous-phase OH oxidation of glyoxal: application of a novel analytical approach employing aerosol mass spectrometry and complementary off-line techniques

Aqueous-phase chemistry of glyoxal may play an important role in the formation of highly oxidized secondary organic aerosol (SOA) in the atmosphere. In this work, we use a novel design of photochemical reactor that allows for simultaneous photo-oxidation and atomization of a bulk solution to study the aqueous-phase OH oxidation of glyoxal. By employing both online aerosol mass spectrometry (AMS) and offline ion chromatography (IC) measurements, glyoxal and some major products including formic acid, glyoxylic acid, and oxalic acid in the reacting solution were simultaneously quantified. This is the first attempt to use AMS in kinetics studies of this type. The results illustrate the formation of highly oxidized products that likely coexist with traditional SOA materials, thus, potentially improving model predictions of organic aerosol mass loading and degree of oxidation. Formic acid is the major volatile species identified, but the atmospheric relevance of its formation chemistry needs to be further investigated. While successfully quantifying low molecular weight organic oxygenates and tentatively identifying a reaction product formed directly from glyoxal and hydrogen peroxide, comparison of the results to the offline total organic carbon (TOC) analysis clearly shows that the AMS is not able to quantitatively monitor all dissolved organics in the bulk solution. This is likely due to their high volatility or low stability in the evaporated solution droplets. This experimental approach simulates atmospheric aqueous phase processing by conducting oxidation in the bulk phase, followed by evaporation of water and volatile organics to form SOA.     

Spectral and photochemical properties of hybrid organic—inorganic nanosystems based on CdS quantum dots and a styrylquinoline ligand

The kinetics of photolysis of a styrylquinoline (SQ) derivative as the photochromic ligand in organic—inorganic hybrid nanosystems (HNSs) with the core composed of CdS quantum dots (QDs) has been studied for the first time as a function of the number of ligand molecules in the HNS shell, which varied from 1 to 10. The hybrid nanosystems have been synthesized in the microwave-assisted mode according to the single-step injection-free procedure. It has been shown that high quantum yields of photoisomerization of the SQ ligand are conserved in the HNS. In the early stages of the photolysis, regardless of the number of SQ ligand molecules in the HNS shell, the kinetics obeys the equation for the photolysis of the monomolecular system (model SQ photochrome) with allowance for the absorption due to QDs as an inert shutter. During the course of long-term photolysis, the quantum dots undergo photodegradation to be completely decomposed. According to the principal component analysis data, several photoproducts with different absorption spectra are formed at the intermediate times of the HNS photolysis.     

Identification of secondary organic aerosols based on aerosol mass spectrometry

Secondary organic aerosol (SOA) is one of the major components of aerosols in the atmosphere and has not been well understood so far. Due to the complex chemical composition of organic aerosols, the identification of SOA has been a hotspot and difficult issue in the field of aerosol study. This study attempts to quantitatively identify SOA in winter of Shenzhen based on positive matrix factorization (PMF) analysis. Major sources were resolved and SOA was identified subsequently according to the characteristic ion fragments measured by highly time-resolved aerosol mass spectrometer measurement. It showed that in the winter of Shenzhen the average SOA concentration was 9.41 ± 6.33 μg/m³, accounting for 39.9 ± 21.8% of the total organic mass. Compared with primary organic aerosol (POA), the SOA concentrations had no large variation, suggestive of characteristics of regional secondary pollutants. The ratio of SOA/BC had pronounced diurnal variation, similar to that of O _x (O₃+NO₂), indicating SOA formation was significantly controlled by activity of photochemistry in the atmosphere. The most effective period for SOA formation was from 9 am ～3 pm since the SOA/BC ratio increased by 122% during this period. This study provides a new technical method and a new idea for SOA investigation.     

Cold-surface photochemistry of primary and tertiary alkyl nitrites

Reflection-absorption infrared spectroscopy (RAIRS) is used to explore the photochemistry of primary and tertiary alkyl nitrites deposited on a gold surface. The primary alkyl nitrites examined for this study were n-butyl, isobutyl, and isopentyl nitrite. These compounds showed qualitatively similar spectra to those observed in previous condensed-phase measurements. The photolysis of the primary nitrites involved the initial formation of an alkoxy radical and NO, followed by production of nitroxyl (HNO) and an aldehydic species. In addition, the formation of nitrous oxide, identified from its distinctive transition near 2230 cm(-1), was observed to form from the self-reaction of nitroxyl. The reaction rates for cis and trans conformer decay, as tracked through their intense N═O stretching modes, were found to be significantly different, potentially due to a structural bias that favors HNO formation for the initial trans conformer photoproducts over recombination. Tert-butyl nitrite demonstrates only the trans conformer in the RAIRS spectra prior to photolysis; however, recombination of the initial NO and RO(?) photoproducts was observed to produce the cis conformer in the photolyzed samples. The primary photoproducts from tert-butyl nitrite can also react to form acetone and nitrosomethane, but the absence of HNO prohibits the formation of N(2)O that was observed for the primary alkyl nitrites. Additionally, the RAIRS spectrum of isobutyl nitrite co-deposited with water was measured to examine the photolysis of this species on a water-ice surface. No change in the identity of the photoproducts was observed in this experiment, and minimal frequency shifting (1-3 cm(-1)) of the vibrational modes occurred. In addition to being a known atmospheric source of NO and various aldehydes, our results point to cold surface processing of alkyl nitrites as a potential environmental source of nitrous oxide.