Ozone removal in the sampling of parts per billion levels of terpenoid compounds: an evaluation of different scrubber materials

Evaluation of offline sampling for atmospheric C3-C11 non-methane hydrocarbons

The concentration variation of C3-C11 non-methane hydrocarbons (NMHCs) collected in several types of commercial flexible bags and adsorption tubes was systematically investigated using a gas chromatography-flame ionization detector (GC-FID) system. The percentage loss of each NMHC in the polyvinyl fluoride (PVF) bags was less than 5% during a 7-hr storage period; significant NMHCs loss was detected in aluminum foil composite film and fluorinated ethylene propylene bags. The thermal desorption efficiency of NMHCs for adsorption tubes filled Carbopack B and Carboxen1000 sorbents was greater than 95% at 300℃, and the loss of NMHCs in the adsorption tubes during 20-days storage at 4℃ was less than 8%. The thermal desorption efficiency for C11 NMHCs in the adsorption tube filled with Carbograph 1 and Carbosieve SⅢ absorbents was less than 40% at 300℃, and pyrolysis of the absorbents at 330℃ interfered significantly with the measurements of some alkenes. The loss of alkenes was significant when NMHCs were sampled by cryo-enrichment at -90℃ in the presence of O₃ for the online NMHC measurements, and negligible for enrichment using adsorption tubes at 25℃. Although O₃ scrubbers have been widely used to eliminate the influence of O₃ on NMHC measurements, the loss of NMHCs with carbon numbers greater than 8 was more than 10%. Therefore, PVF bags and adsorption tubes filled Carbopack B and Carboxen1000 sorbents were recommended for the sampling of atmospheric NMHCs.

An Improvement of SPME-Based Sampling Technique to Collect Volatile Organic Compounds from Quercus ilex at the Environmental Level

Biogenic Volatile Organic Compounds (BVOCs) include many chemical compounds emitted by plants into the atmosphere. These compounds have a great effect on biosphere-atmosphere interactions and may affect the concentration of atmospheric pollutants, with further consequences on human health and forest ecosystems. Novel methods to measure and determine BVOCs in the atmosphere are of compelling importance considering the ongoing climate changes. In this study, we developed a fast and easy-to-handle analytical methodology to sample these compounds in field experiments using solid-phase microextraction (SPME) fibers at the atmospheric level. An improvement of BVOCs adsorption from SPME fibers was obtained by coupling the fibers with fans to create a dynamic sampling system. This innovative technique was tested sampling Q. ilex BVOCs in field conditions in comparison with the conventional static SPME sampling technique. The results showed a great potential of this dynamic sampling system to collect BVOCs at the atmosphere level, improving the efficiency and sensitivity of SPME fibers. Indeed, our novel device was able to reduce the sampling time, increase the amount of BVOCs collected through the fibers and add information regarding the emissions of these compounds at the environmental level.

Pollination in the Anthropocene: a Moth Can Learn Ozone-Altered Floral Blends

Insect pollination is essential to many unmanaged and agricultural systems and as such is a key element in food production. However, floral scents that pollinating insects rely on to locate host plants may be altered by atmospheric oxidants, such as ozone, potentially making these cues less attractive or unrecognizable to foraging insects and decreasing pollinator efficacy. We demonstrate that levels of tropospheric ozone commonly found in many rural areas are sufficient to disrupt the innate attraction of the tobacco hawkmoth Manduca sexta to the odor of one of its preferred flowers, Nicotiana alata. However, we further find that visual navigation together with associative learning can offset this disruption. Foraging moths that initially find an ozone-altered floral scent unattractive can target an artificial flower using visual cues and associate the ozone-altered floral blend with a nectar reward. The ability to learn ozone-altered floral odors may enable pollinators to maintain communication with their co-evolutionary partners and reduce the negative impacts that anthropogenically elevated oxidants may have on plant-pollinator systems.

Vertical profiles of biogenic volatile organic compounds as observed online at a tower in Beijing

Vertical profiles of isoprene and monoterpenes were measured by a proton transfer reaction-time of flight-mass spectrometry (PTR-ToF-MS) at heights of 3, 15, 32, 64, and 102 m above the ground on the Institute of Atmospheric Physics (IAP) tower in central Beijing during the winter of 2016 and the summer of 2017. Isoprene mixing ratios were larger in summer due to much stronger local emissions whereas monoterpenes were lower in summer due largely to their consumption by much higher levels of ozone. Isoprene mixing ratios were the highest at the 32 m in summer (1.64 ± 0.66 ppbV) and at 15 m in winter (1.41 ± 0.64 ppbV) with decreasing concentrations to the ground and to the 102 m, indicating emission from the tree canopy of the surrounding parks. Monoterpene mixing ratios were the highest at the 3 m height in both the winter (0.71 ± 0.42 ppbV) and summer (0.16 ± 0.10 ppbV) with a gradual decreasing trend to 102 m, indicting an emission from near the ground level. The lowest isoprene and monoterpene mixing ratios all occurred at 102 m, which were 0.71 ± 0.42 ppbV (winter) and 1.35 ± 0.51 ppbV (summer) for isoprene, and 0.42 ± 0.22 ppbV (winter) and 0.07 ± 0.06 ppbV (summer) for monoterpenes. Isoprene in the summer and monoterpenes in the winter, as observed at the five heights, showed significant mutual correlations. In the winter monoterpenes were positively correlated with combustion tracers CO and acetonitrile at 3 m, suggesting possible anthropogenic sources.

Chemical kinetics of multiphase reactions between ozone and human skin lipids: Implications for indoor air quality and health effects

Ozone reacts with skin lipids such as squalene, generating an array of organic compounds, some of which can act as respiratory or skin irritants. Thus, it is important to quantify and predict the formation of these products under different conditions in indoor environments. We developed the kinetic multilayer model that explicitly resolves mass transport and chemical reactions at the skin and in the gas phase (KM-SUB-Skin). It can reproduce the concentrations of ozone and organic compounds in previous measurements and new experiments. This enabled the spatial and temporal concentration profiles in the skin oil and underlying skin layers to be resolved. Upon exposure to ~30 ppb ozone, the concentrations of squalene ozonolysis products in the gas phase and in the skin reach up to several ppb and on the order of ~10 mmol m^-3 . Depending on various factors including the number of people, room size, and air exchange rates, concentrations of ozone can decrease substantially due to reactions with skin lipids. Ozone and dicarbonyls quickly react away in the upper layers of the skin, preventing them from penetrating deeply into the skin and hence reaching the blood.

WITHDRAWN: Wet effluent diffusion denuder: The tool for determination of monoterpenes in forest

The Publisher regrets that this article is an accidental duplication of an article that has already been published, 10.1016/j.talanta.2016.03.032. The duplicate article has therefore been withdrawn.The full Elsevier Policy on Article Withdrawal can be found at http://www.elsevier.com/locate/withdrawalpolicy.

Use of a versatile high efficiency multiparallel denuder for the sampling of PAHs in ambient air: gas and particle phase concentrations, particle size distribution and artifact formation

The design and performance of a multiparallel plate denuder able to operate at low and high-flow (3-30 L/min) for the collection of polycyclic aromatic hydrocarbon (PAH) vapor is described. The denuder, in combination with a micro orifice uniform deposit impactor (MOUDI) was used to assess processes of artifact formation in MOUDIs used with and without an upstream denuder. Duplicate sampling trains with an upstream denuder showed good repeatability of the measured gas and particle-phase concentrations and low breakthrough in the denuder (3.5-15%). The PAH size distributions within undenuded and denuded MOUDIs were studied. Use of the denuder altered the measured size distribution of PAHs toward smaller sizes, but both denuded and undenuded systems are subject to sampling artifacts.

C60 oxide as a key component of aqueous C60 colloidal suspensions

Stable aqueous fullerene colloidal suspensions (nC(60)) are demonstrated to rely on the [6,6]-closed epoxide derivative of the fullerene (C(60)O) for stability. This derivative is present, though often unrecognized, in small quantities in nearly all C(60) starting materials due to a reaction with air. The low-yield formation of nC(60) from organic solvent solutions results from a preferential partitioning and thus enrichment of C(60)O in the colloidal particles. This partitioning is significantly retarded in the nC(60) synthesis method that does not involve organic solvent solutions: long-term stirring in water. Instead, this method relies on trace levels of ozone in the ambient atmosphere to produce sufficient C(60)O at the surfaces of the nC(60) particles to allow stable suspension in water. Controlled-atmosphere syntheses, deliberate C(60)O enrichment, light scattering measurements, and extraction followed by HPLC analysis and UV-visible absorption spectroscopy support the above model of nC(60) formation and stabilization.

QCM-arrays for sensing terpenes in fresh and dried herbs via bio-mimetic MIP layers

A piezoelectric 10 MHz multichannel quartz crystal microbalance (MQCM), coated with six molecularly imprinted polystyrene artificial recognition membranes have been developed for selective quantification of terpenes emanated from fresh and dried Lamiaceae family species, i.e., rosemary (Rosmarinus Officinalis L.), basil (Ocimum Basilicum) and sage (Salvia Officinalis). Optimal e-nose parameters, such as layer heights (1-6 KHz), sensitivity <20 ppm of analytes, selectivity at 50 ppm of terpenes, repeatability and reproducibility were thoroughly adjusted prior to online monitoring. Linearity in reversible responses over a wide concentration range <20-250 ppm has been achieved. Discrimination between molecules of similar molar masses, even for isomers, e.g. α-pinene and β-pinene is possible. The array has proven its sensitive and selective properties of sensor responses (20-1,200 Hz) for the difference of fresh and dried herbs. The sensor data attained was validated by GC-MS, to analyze the profiles of sensor emanation patterns. The shelf-life of herbs was monitored via emanation of organic volatiles during a few days. Such an array in association with data analysis tools can be utilized for characterizing complex mixtures.

Reactions of ozone with human skin lipids: sources of carbonyls, dicarbonyls, and hydroxycarbonyls in indoor air

This study has used proton transfer reaction-mass spectrometry (PTR-MS) for direct air analyses of volatile products resulting from the reactions of ozone with human skin lipids. An initial series of small-scale in vitro and in vivo experiments were followed by experiments conducted with human subjects in a simulated office. The latter were conducted using realistic ozone mixing ratios (approximately 15 ppb with occupants present). Detected products included mono- and bifunctional compounds that contain carbonyl, carboxyl, or alpha-hydroxy ketone groups. Among these, three previously unreported dicarbonyls have been identified, and two previously unreported alpha-hydroxy ketones have been tentatively identified. The compounds detected in this study (excepting acetone) have been overlooked in surveys of indoor pollutants, reflecting the limitations of the analytical methods routinely used to monitor indoor air. The results are fully consistent with the Criegee mechanism for ozone reacting with squalene, the single most abundant unsaturated constituent of skin lipids, and several unsaturated fatty acid moieties in their free or esterified forms. Quantitative product analysis confirms that squalene is the major scavenger of ozone at the interface between room air and the human envelope. Reactions between ozone and human skin lipids reduce the mixing ratio of ozone in indoor air, but concomitantly increase the mixing ratios of volatile products and, presumably, skin surface concentrations of less volatile products. Some of the volatile products, especially the dicarbonyls, may be respiratory irritants. Some of the less volatile products may be skin irritants.

Reduction of biogenic VOC sampling losses from ozone via trans-2-butene addition

The continuous addition of trans-2-butene to air containing ozone-reactive volatile and semivolatile organic compounds prior to sampling on Tenax-TA adsorbent was found to be an effective means of removing ozone and reducing analyte losses of ozone reactive biogenic volatile organic compounds (BVOCs). To allow sufficient time for ozone scavenging to occur, the reacting mixture is passed through a heated (40 degrees C) coil of Sulfinert (Restek Corp., Bellefonte, PA) treated stainless steel tubing. The method was evaluated using a test mixture consisting of terpenes, terpenoid alcohols, and sesquiterpenes at part per trillion (pptv) levels in air in the presence of 100 parts per billion (ppbv) of ozone. The continuous addition of trans-2-butene to produce 600 ppm (ppmv) was found to be completely effective in controlling VOC losses on Tenax-TA as long as (1) sufficient time is allowed for the ozone scavenging to occur before the VOCs are adsorbed and (2) analyte enrichment on the adsorbentdoes not approach the hydroxyl radical scavenging capacity of the trans-2-butene. A manganese dioxide (MnO2) coated copper screen ozone scrubber was also tested and found to be of very limited utility.

Approaches for quantifying reactive and low-volatility biogenic organic compound emissions by vegetation enclosure techniques - part A

The high reactivity and low vapor pressure of many biogenic volatile organic compounds (BVOC) make it difficult to measure whole-canopy fluxes of BVOC species using common analytical techniques. The most appropriate approach for estimating these BVOC fluxes is to determine emission rates from dynamic vegetation enclosure measurements. After scaling leaf- and branch-level emission rates to the canopy level, these fluxes can then be used in models to determine BVOC influences on atmospheric chemistry and aerosol processes. Previously published reports from enclosure measurements show considerable variation among procedures with limited guidelines or standard protocols to follow. This article reviews this literature and describes the variety of enclosure types, materials, and analysis techniques that have been used to determine BVOC emission rates. The current review article is followed by a companion paper which details a comprehensive enclosure technique that incorporates both recommendations from the literature as well as insight gained from theoretical calculations and practical experiences. These methods have yielded new BVOC emission data for highly reactive monoterpenes (MT) and sesquiterpenes (SQT) from a variety of vegetation species.

Heterogeneous reactions of ozone and D-limonene on activated carbon

If released in significant amounts, products formed by reactions between ozone (O3) and volatile organic compounds (VOCs) sorbed on activated carbon (AC) filters could degrade indoor air quality (IAQ). Heterogeneous reactions were investigated in laboratory experiments aimed at characterizing reaction products. Effluent air of AC loaded with limonene and exposed to O3 (5.8 ppm) yielded unreacted limonene (501+/-197 microg/m3), low levels of 4-acetyl-1-methylcyclohexene (AMCH) (20+/-2 microg/m3), and limonene oxides (25+/-7 microg/m3). Most of the O3-limonene products remained on the AC, and most (58%) of the limonene remained unreacted on the AC after exposure to a stoichiometric excess of O3 for 48 h. Thus, in addition to known homogenous reactions, O3-limonene reactions occur heterogeneously on AC but to a much lesser extent. However, the fate of 95% of the depleted limonene was not determined; much of the missing portion was attributed to desorption from the AC, but the formation of other secondary indoor air pollutants is possible. VOC-loaded AC air filters exposed to O3 seem unlikely, however, to constitute a significant emission source of reaction products. More studies are necessary to investigate other pollutants, effects of environmental conditions, and VOC releases from AC that may be enhanced by O3 exposure.

PRACTICAL IMPLICATIONS

Reactions between ozone and certain volatile organic compounds such as limonene (a common ingredient of many consumer products) occurring on the surface of ventilation filters could impact indoor air quality if products are released in significant amounts. This study suggests that although very small amounts of limonene adsorbed on a filter will react with O3, ventilation filters are not likely to be significant sources of ozone oxidation products. More studies are needed to investigate whether ozone exposure enhances desorption of pollutants from ventilation filters and to measure the formation of formaldehyde and other products that are not easily retained by charcoal filters.

Ozone-initiated chemistry in an occupied simulated aircraft cabin

We have used multiple analytical methods to characterize the gas-phase products formed when ozone was added to cabin air during simulated 4-hour flights that were conducted in a reconstructed section of a B-767 aircraft containing human occupants. Two separate groups of 16 females were each exposed to four conditions: low air exchange (4.4 (h-1)), <2 ppb ozone; low air exchange, 61-64 ppb ozone; high air exchange (8.8 h(-1)), <2 ppb ozone; and high air exchange, 73-77 ppb ozone. The addition of ozone to the cabin air increased the levels of identified byproducts from approximately 70 to 130 ppb at the lower air exchange rate and from approximately 30 to 70 ppb at the higher air exchange rate. Most of the increase was attributable to acetone, nonanal, decanal, 4-oxopentanal (4-OPA), 6-methyl-5-hepten-2-one (6-MHO), formic acid, and acetic acid, with 0.25-0.30 mol of quantified product volatilized per mol of ozone consumed. Several of these compounds reached levels above their reported odor thresholds. Most byproducts were derived from surface reactions with occupants and their clothing, consistent with the inference that occupants were responsible for the removal of >55% of the ozone in the cabin. The observations made in this study have implications for other indoor settings. Whenever human beings and ozone are simultaneously present, one anticipates production of acetone, nonanal, decanal, 6-MHO, geranyl acetone, and 4-OPA.

Oxidant denuder sampling for analysis of polycyclic aromatic hydrocarbons and their oxygenated derivates in ambient aerosol: evaluation of sampling artefact

The concentrations of some polycyclic aromatic hydrocarbons (PAH) and oxygenated PAH (O-PAH) can be changed by oxidation reactions during sampling. This can lead to an over- or underestimation of the corresponding adverse health effects. The aim of this study was the evaluation of these sampling artefacts. The potential of using an oxidant denuder was shown by parallel low-volume sampling with and without MnO(2) ozone denuder. Twenty-three PAH and 11 O-PAH in ambient air were analysed, both in the vapour and particulate phase. The denuder was proven to be highly efficient for stripping ozone from air while causing no significant particle losses. In general, the concentrations of 5- to 7-ring PAH, which are predominantly associated with particles, were underestimated in non-denuded samples. The highest losses due to reaction with ozone and other atmospheric oxidants were observed for benzo[a]pyrene and perylene. Concurrently, the concentrations of most of the mainly particle-associated 4- to 5-ring O-PAH were higher in the non-denuded samples. The denuder did not only remove ozone, moreover other gaseous species such as more volatile PAH and O-PAH were partially oxidized on the catalytic surface, too. Degradation of PAH and concurrent degradation/formation reactions of O-PAH occurred. The corresponding reactivities of selected PAH and O-PAH are discussed.

Analysis of atmospheric sesquiterpenes: sampling losses and mitigation of ozone interferences

Atmospheric standards containing parts-per-billion levels of 14 semivolatile hydrocarbon compounds, including eight sesquiterpenes (SQTs) (longipinene, alpha-copaene, isolongifolene, alpha-cedrene, trans-caryophyllene, aromadendrene, alpha-humulene, delta-cadinene), two oxidized sesquiterpenoids (cisnerolidol, trans-nerolidol), one biogenic ketone (geranylacetone) and three aromatic compounds (1,3,5-triisopropylbenzene, diphenylmethane, nonylbenzene), were collected onto four solid adsorbent materials at increasing ozone mixing ratios (0-100 ppbv 03) for analysis by thermodesorption-gas chromatography. Substantial sampling losses of up to >90% were found for the most reactive SQT, even at the lowest ozone level investigated of 20 ppbv. Loss rates from the ozone-SQT reaction were used to derive estimates of gas-phase ozone reaction rate constants for longipinene, alpha-copaene, isolongifolene, geranylacetone, aromadendrene, delta-cadinene, cis-nerolidol, and transnerolidol. Three different ozone mitigation techniques were investigated to prevent these sampling losses. These strategies included (a) placing glass fiber filters impregnated with sodium thiosulfate (Na2S2O3) into the sampling line, (b) titration of ozone in the sampling stream with nitric oxide (NO), and (c) catalytically removing ozone with a commercially available manganese dioxide (MnO2) catalyst. All three techniques reduced ozone-mixing ratios from 100 ppbv to <0.6 ppbv at sampling flow rates of 1 L min(-1). When the Na2S2O3 filters and the NO-titration techniques were applied, SQT loss rates decreased from 25-60% to 0-5% for most SQT compounds and from >90% to approximately 10-50% for the two most reactive compounds at ozone mixing ratios of up to 100 ppbv. The commercial manganese dioxide scrubber, however, caused complete analyte losses (>98%) even at 0 ppbv ozone. These results underline the need and present applicable techniques for removal of ozone in air samples for SQT analysis by solid adsorption techniques.

Products of ozone-initiated chemistry in a simulated aircraft environment

We used proton-transfer-reaction mass spectrometry (PTR-MS) to examine the products formed when ozone reacted with the materials in a simulated aircraft cabin, including a loaded high-efficiency particulate air (HEPA) filter in the return air system. Four conditions were examined: cabin (baseline), cabin plus ozone, cabin plus soiled T-shirts (surrogates for human occupants), and cabin plus soiled T-shirts plus ozone. The addition of ozone to the cabin without T-shirts, at concentrations typically encountered during commercial air travel, increased the mixing ratio (v:v concentration) of detected pollutants from 35 ppb to 80 ppb. Most of this increase was due to the production of saturated and unsaturated aldehydes and tentatively identified low-molecular-weight carboxylic acids. The addition of soiled T-shirts, with no ozone present, increased the mixing ratio of pollutants in the cabin air only slightly, whereas the combination of soiled T-shirts and ozone increased the mixing ratio of detected pollutants to 110 ppb, with more than 20 ppb originating from squalene oxidation products (acetone, 4-oxopentanal, and 6-methyl-5-hepten-2-one). For the two conditions with ozone present, the more-abundant oxidation products included acetone/propanal (8-20 ppb), formaldehyde (8-10 ppb), nonanal (approximately 6 ppb), 4-oxopentanal (3-7 ppb), acetic acid (approximately 7 ppb), formic acid (approximately 3 ppb), and 6-methyl-5-hepten-2-one (0.5-2.5 ppb), as well as compounds tentatively identified as acrolein (0.6-1 ppb) and crotonaldehyde (0.6-0.8 ppb). The odor thresholds of certain products were exceeded. With an outdoor air exchange of 3 h(-1) and a recirculation rate of 20 h(-1), the measured ozone surface removal rate constant was 6.3 h(-1) when T-shirts were not present, compared to 11.4 h(-1) when T-shirts were present.

A dynamic dilution system-based evaluation of the procedure adopted for determining ozone precursor volatile compounds

A dynamic dilution system was created to evaluate the performance and the reliability of ozone precursor volatile organic compound (VOC) sampling ("TO-Can" canisters) and analysis (thermal desorption/gas chromatography/flame ionisation detection) techniques used by the "Laboratoire Interregional de Chimie du Grand Est (LIC)". Different atmospheres of VOCs were generated at concentrations between 0.8 and 25 ppb, with temperatures of 0, 10, 20 and 30 degrees C, and with relative humidities of 0, 30, 50, 70 and 90%. These conditions are generally representative of those commonly observed in ambient air in the eastern France. This dynamic dilution allows the simulation of a wide range of scenarios (concentrations, temperatures and relative humidities). After assessing the capacity and performance of the system, it was applied in order to evaluate the recoveries and stabilities of VOCs from canisters used for the collection and analysis of two mixtures of VOCs. The first mixture contained six alkanes (ethane, propane, butane, pentane, hexane and heptane), and the second contained five alkenes (ethene, propene, butene, 1-pentene and 1-hexene), five aromatics (benzene, toluene, ethylbenzene, m-xylene and o-xylene), acetylene, and 1,3-butadiene. No significant losses of alkanes from the canisters were observed after 21 days of storage, and good recoveries of alkanes from the canisters (>80%) were obtained regardless of the concentration, the temperature and the relative humidity. However, losses of certain aromatics were noted at low relative humidity.

Full-scale chamber investigation and simulation of air freshener emissions in the presence of ozone

Volatile organic compound (VOC) emissions from one electrical plug-in type of pine-scented air freshener and their reactions with O3 were investigated in the U.S. Environmental Protection Agency indoor air research large chamber facility. Ozone was generated from a device marketed as an ozone generator air cleaner. Ozone and oxides of nitrogen concentrations and chamber conditions such as temperature, relative humidity, pressure, and air exchange rate were controlled and/or monitored. VOC emissions and some of the reaction products were identified and quantified. Source emission models were developed to predict the time/concentration profiles of the major VOCs (limonene, alpha-pinene, beta-pinene, 3-carene, camphene, benzyl propionate, benzyl alcohol, bornyl acetate, isobornyl acetate, and benzaldehyde) emitted bythe air freshener. Gas-phase reactions of VOCs from the air freshener with O3 were simulated by a photochemical kinetics simulation system using VOC reaction mechanisms and rate constants adopted from the literature. The concentration-time predictions were in good agreement with the data for O3 and VOCs emitted from the air freshener and with some of the primary reaction products. Systematic differences between the predictions and the experimental results were found for some species. Poor understanding of secondary reactions and heterogeneous chemistry in the chamber is the likely cause of these differences. The method has the potential to provide data to predict the impact of O3/VOC interactions on indoor air quality.

Ozone reaction with n-aldehydes (n=4-10), benzaldehyde, ethanol, isopropanol, and n-propanol adsorbed on a dual-bed graphitized carbon-carbon molecular sieve adsorbent cartridge

Ozone reacts with n-aldehydes (n=4-10), benzaldehyde, ethanol, isopropanol and n-propanol adsorbed on a dual-bed graphitized carbon-carbon molecular sieve adsorbent cartridge. Destruction of n-aldehydes increases with n number and with ozone concentration. In some sampling experiments both generation and destruction of n-aldehydes by ozone are observed. In field experiments the results of sample analysis for n-aldehydes and benzaldehyde are frequently not proportional to sample volume whereas results for toluene and isoprene, and sometimes for total carbon, are. A simple theory is developed to simulate the net result of three processes: the adsorption of compounds from an air stream onto a solid adsorbent, the generation of compounds by reaction of ozone with materials upstream of or on the adsorbent, and the destruction by ozone of pre-existing compounds and compounds adsorbed from the sample stream. The use of distributed volume pairs is recommended as a way to identify loss of sample integrity during air monitoring experiments.