Photolysis Lifetime Research Articles

UV-spectrum and photodecomposition of peroxynitrous acid in the troposphere.

The UV spectrum of peroxynitrous acid, HOONO, was computed at the B3LYP/AVTZ and MCSCF/AVTZ levels using the fewest switches surface hopping algorithm. Due to large-amplitude vibrational motions of this molecule, the maxima in the simulated spectra are displaced from the positions of vertical excitations. The three lowest excited electronic singlet states, which are all repulsive, can be reached by UV absorption. The photolysis products are determined, and the photolysis rate constant is provided for the first time. We found that near the tropopause the photolysis rate constant J ≈ 6 × 10-4 s-1, exceeds that for thermal decomposition by two orders of magnitude. The photolysis lifetime is about 30 minutes. Thus, photolysis is an important process and should be included in atmospheric models.

Exposure and Toxicity of Polybrominated Diphenyl Ethers: A Mini Review

Polybrominated Diphenyl Ethers (PBDEs), recognized as persistent organic pollutants by the United Nations Environment Programme, are a class of brominated flame retardants that pose significant environmental and health risks. These compounds, consisting of two aromatic rings with up to 10 bromine atom substitutions, are categorized into penta-BDE, octa-BDE, and deca-BDE based on their bromine content, each exhibiting distinct environmental behaviors. PBDEs with fewer bromine atoms are more volatile and prone to bioaccumulation, raising significant health concerns. These compounds, often added physically to products, can leach into the environment, leading to pollution during production and after the parent polymer degrades. The transformation of higher brominated diphenyl ethers into less brominated forms in the environment further complicates their impact, with mono-brominated BDE-3 being particularly concerning due to its extended atmospheric photolysis lifetime and increased bioavailability. The management of PBDEs is challenging due to their persistence and transformation in the environment. As endocrine disruptors, they are linked to various acute and chronic toxicological effects, including neurodevelopmental toxicity, teratogenicity, and potential carcinogenicity. Their structural similarity to thyroid hormones allows them to disrupt thyroid hormone balance, leading to further health complications. The subject of this review is to summarize the current body of knowledge that is essential to understand their long-term effects on ecosystems and human health and to develop strategies to mitigate their adverse impacts.

The electronic structure of 2(5H)-thiophenone investigated by vacuum ultraviolet synchrotron radiation and theoretical calculations

The electronic state spectroscopy of 2(5H)-thiophenone, C4H4OS, has been investigated by high-resolution vacuum ultraviolet photoabsorption in the 3.76–10.69 eV energy range using synchrotron radiation, together with novel quantum chemical calculations performed at the equation of motion coupled cluster singles and doubles (EOM-CCSD) level of theory. The major electronic transitions have been assigned to valence and Rydberg character, with relevant C=O, C=C and C–C stretching vibrations across the entire absorption spectrum. Photolysis lifetimes in the Earth’s atmosphere (0–50 km altitude) have been estimated from the absolute photoabsorption cross-sections, indicating that solar photolysis can be expected to be a strong sink mechanism.Graphical abstract

Valence and Rydberg excitations of 3-fluorotoluene in the 4.4–10.8 eV photoabsorption energy region

The absolute photoabsorption cross sections for 3-fluorotoluene in the 4.4–10.8 eV energy-range were obtained for the first-time using a synchrotron radiation light source. New theoretical calculations, providing vertical excitation energies and oscillator strengths, were performed at the time-dependent density functional theory and the equation-of-motion coupled cluster method restricted to single and double excitations to qualitatively support the experimental data. The electronic transitions discernible in the photoabsorption spectrum have been assigned to valence, mixed valence-Rydberg and Rydberg transitions. Additionally, a comprehensive assignment of the vibronic structure was performed with the main contribution of C–H in plane bending mode progressions dictating the spectroscopy of the lowest-lying absorption band. From the absolute photoabsorption cross sections, the photolysis lifetimes of 3-fluorotoluene in the Earth's atmosphere were also obtained.

High Chlorine Concentrations in an Unconventional Oil and Gas Development Region and Impacts on Atmospheric Chemistry.

Growth in unconventional oil and gas development (UOGD) in the United States has increased airborne emissions, raising environmental and human health concerns. To assess the potential impacts on air quality, we deployed instrumentation in Karnes City, Texas, a rural area in the middle of the Eagle Ford Shale. We measured several episodes of elevated Cl2 levels, reaching maximum hourly averages of 800 ppt, the highest inland Cl2 concentration reported to date. Concentrations peak during the day, suggesting a strong local source (given the short photolysis lifetime of Cl2) and/or a photoinitiated production mechanism. Well preproduction activity near the measurement site is a plausible source of these high Cl2 levels via direct emission and photoactive chemistry. ClNO2 is also observed, but it peaks overnight, consistent with well-known nocturnal formation processes. Observations of organochlorines in the gas and particle phases reflect the contribution of chlorine chemistry to the formation of secondary pollutants in the area. Box modeling results suggest that the formation of ozone at this location is influenced by chlorine chemistry. These results suggest that UOGD can be an important source of reactive chlorine in the atmosphere, impacting radical budgets and the formation of secondary pollutants in these regions.

Valence and Rydberg excitations of 2-fluorotoluene in the 4.4–10.8 eV photoabsorption energy region

The electronic state spectroscopy of 2-fluorotoluene in the gas phase has been investigated for the first time using high-resolution vacuum ultraviolet photoabsorption experiments in the 4.4–10.8 eV energy-range, with absolute cross-section measurements obtained. Additionally, we also present a novel set of ab initio calculations (vertical excitation energies and oscillator strengths) at two different levels of theory, equation-of-motion coupled-cluster singles and doubles (EOM-CCSD) and time-dependent density functional theory (TD-DFT). These are used in the assignment of valence, mix valence-Rydberg and Rydberg transitions, with the associated vibronic series analysed. The measured absolute photoabsorption cross-sections have been used to calculate the photolysis lifetime of 2-fluorotoluene in the Earth's atmosphere.

Electronic State Spectroscopy of Nitromethane and Nitroethane.

High-resolution photoabsorption cross-sections in the 3.7-10.8 eV energy range are reinvestigated for nitromethane (CH3NO2), while for nitroethane (C2H5NO2), they are reported for the first time. New absorption features are observed for both molecules which have been assigned to vibronic excitations of valence, Rydberg, and mixed valence-Rydberg characters. In comparison with nitromethane, nitroethane shows mainly broad absorption bands with diffuse structures, which can be interpreted as a result of the side-chain effect contributing to an increased number of internal degrees of freedom. New theoretical quantum chemical calculations performed at the time-dependent density functional theory (TD-DFT) level were used to qualitatively help interpret the recorded photoabsorption spectra. From the photoabsorption cross-sections, photolysis lifetimes in the terrestrial atmosphere have been obtained for both compounds. Relevant internal conversion from Rydberg to valence character is noted for both molecules, while the nuclear dynamics of CH3NO2 and C2H5NO2 along the C-N reaction coordinate have been evaluated through potential energy curves at the TD-DFT level of theory, showing that the pre-dissociative character is more prevalent in nitromethane than in nitroethane.

Electronically excited states of formic acid investigated by theoretical and experimental methods

Absolute cross-section values are reported from high-resolution vacuum ultraviolet (VUV) photoabsorption measurements of gas-phase formic acid (HCOOH) in the photon energy range 4.7–10.8 eV (265–115 nm), together with quantum chemical calculations to provide vertical energies and oscillator strengths. The combination of experimental and theoretical methods has allowed a comprehensive assignment of the electronic transitions. The VUV spectrum reveals various vibronic features not previously reported in the literature, notably associated with (3pa′←10a′), (3p′a′←10a′), (3sa′←2a″) and (3pa′←2a″) Rydberg transitions. The assignment of vibrational features in the absorption bands reveal that the C=O stretching, v3′a′, the H′–O–C′ deformation, v5′a′, the C–O stretching, v6′a′, and the O=C–O′ deformation, v7′a′ modes are mainly active. The measured absolute photoabsorption cross sections have also been used to estimate the photolysis lifetime of HCOOH in the upper stratosphere (30–50 km), showing that solar photolysis is an important sink at altitudes above 30 km but not in the troposphere. Potential energy curves for the lowest-lying electronic excited states, as a function of the C=O coordinate, are obtained employing time dependent density functional theory (TD-DFT). These calculations have shown the relevance of internal conversion from Rydberg to valence character governing the nuclear dynamics, yielding clear evidence of the rather complex multidimensional nature of the potential energy surfaces involved.

The electronic spectra of 2- chlorothiophene and 3-chlorothiophene in the vacuum ultraviolet photoabsorption energy region (3.9–10.8 eV)

The absolute photoabsorption cross-sections for 2-chlorothiophene (2-Cl-Th) and 3-chlorothiophene (3-Cl-Th), in the 3.9–10.8 eV energy range, were recorded for the first-time using synchrotron radiation. New ab initio theoretical calculations performed at the time-dependent density functional theory (TD-DFT) level were used to help interpret the photoabsorption spectra. These have provided important information on the nature of the excited states which have been assigned to valence, mixed valence-Rydberg and Rydberg transitions. The combination of high-resolution vacuum ultra-violet synchrotron radiation with TD-DFT, represents the most comprehensive and self-consistent assignment of the chlorothiophenes electronic excitation to date. Photolysis lifetimes in the Earth^{\\prime}s upper atmosphere for both chemical compounds have been estimated from the absolute photoabsorption cross-sections. Potential energy curves have been obtained at the TD-DFT level of theory, showing that the dissociative character of the lowest-lying electronic states is more efficient in 3-Cl-Th.

UV absorption spectrum of monochlorodimethyl sulfide (CH3SCH2Cl)

Monochlorodimethyl sulfide (CH3SCH2Cl, MCDMS) is a trace gas thought to be formed in the marine environment via the reaction of Cl2 with dimethyl sulfide (DMS, CH3SCH3) with implications for the temporal and spatial production of SO2 and sulfate aerosol formation. In this study, the room temperature UV absorption spectrum of MCDMS in the 200–330 nm wavelength region was measured. The spectrum measured in this work differs significantly in the long-wavelength actinic region, >295 nm, from that reported previously by Copeland et al. (Environ. Sci. Technol., 2014, 48, 1557–1565). On the basis of the present results, the MCDMS first-order tropospheric photolysis rate coefficient is a factor of ∼250 less than reported in Copeland et al. The diurnally averaged MCDMS photolysis lifetime is estimated to be ∼125 days at ground level for Summer mid-latitude conditions over the ocean. UV photolysis is, most likely, a minor gas-phase degradation pathway for MCDMS compared to its OH radical and Cl-atom reactive losses.

Direct photolysis of contaminants in surface freshwaters, within the equivalent monochromatic wavelength (EMW) approximation

Abiotic photochemical reactions are usually very important degradation pathways for biorecalcitrant pollutants in surface freshwaters. Therefore, the assessment of photolytic lifetimes of contaminants helps estimate their impact on aquatic systems. This is commonly carried out by combining irradiation experiments and modelling, where the latter considers mathematical functions with polychromatic parameters, such as sunlight spectra, photolysis quantum yields (when Kasha's rule does not hold), and absorption coefficients. With the polychromatic approach, the photolytic lifetime is calculated by solving several integrals, which requires quite demanding modelling resources. In this work, we applied a recently developed approach, which is based on the equivalent monochromatic wavelength (EMW) approximation, to compute the direct-photolysis lifetimes of a range of >40 pollutants in inland waters. The EMW approximation allowed for easier modelling procedure, at the same time providing very good agreement with the polychromatic system. To further show EMW potentialities, lifetimes of three contaminants were mapped over the Piedmont region (NW Italy), as an example of how easy it becomes to geographically EMW-assess the potential of watercourses, to get photochemically decontaminated from pollutants.

OH Radical and Chlorine Atom Kinetics of Substituted Aromatic Compounds: 4-chlorobenzotrifluoride (p-ClC6H4CF3).

The mechanisms for the OH radical and Cl atom gas-phase reaction kinetics of substituted aromatic compounds remain a topic of atmospheric and combustion chemistry research. 4-Chlorobenzotrifluoride (p-chlorobenzotrifluoride, p-ClC6H4CF3, PCBTF) is a commonly used substituted aromatic volatile organic compound (VOC) in solvent-based coatings. As such, PCBTF is classified as a volatile chemical product (VCP) whose release into the atmosphere potentially impacts air quality. In this study, rate coefficients, k1, for the OH + PCBTF reaction were measured over the temperature ranges 275-340 and 385-940 K using low-pressure discharge flow-tube reactors coupled with a mass spectrometer detector in the ICARE/CNRS (Orléans, France) laboratory. k1(298-353 K) was also measured using a relative rate method in the thermally regulated atmospheric simulation chamber (THALAMOS; Douai, France). k1(T) displayed a non-Arrhenius temperature dependence with a negative temperature dependence between 275 and 385 K given by k1(275-385 K) = (1.50 ± 0.15) × 10-14 exp((705 ± 30)/T) cm3 molecule-1 s-1, where k1(298 K) = (1.63 ± 0.03) × 10-13 cm3 molecule-1 s-1 and a positive temperature dependence at elevated temperatures given by k1(470-950 K) = (5.42 ± 0.40) × 10-12 exp(-(2507 ± 45) /T) cm3 molecule-1 s-1. The present k1(298 K) results are in reasonable agreement with two previous 296 K (760 Torr, syn. air) relative rate measurements. The rate coefficient for the Cl-atom + PCBTF reaction, k2, was also measured in THALAMOS using a relative rate technique that yielded k2(298 K) = (7.8 ± 2) × 10-16 cm3 molecule-1 s-1. As part of this work, the UV and infrared absorption spectra of PCBTF were measured (NOAA; Boulder, CO, USA). On the basis of the UV absorption spectrum, the atmospheric instantaneous UV photolysis lifetime of PCBTF (ground level, midlatitude, Summer) was estimated to be 3-4 days, assuming a unit photolysis quantum yield. The non-Arrhenius behavior of the OH + PCBTF reaction over the temperature range 275 to 950 K is interpreted using a mechanism for the formation of an OH-PCBTF adduct and its thermochemical stability. The results from this study are included in a discussion of the OH radical and Cl atom kinetics of halogen substituted aromatic compounds for which only limited temperature-dependent kinetic data are available.

Low-lying electronic states of ethanol investigated by theoretical and synchrotron radiation methods

We investigate the ethanol absorption spectrum in the range 5.64–10.78 eV (220–115 nm), by combining ab initio theoretical and experimental methods in order to provide the most accurate and up-to-date information about the electronic state spectroscopy of ethanol. In particular, absolute cross-section values are reported from high-resolution vacuum ultraviolet (VUV) photoabsorption measurements. The present VUV spectrum reveals several new features not previously reported in the literature, with particular reference to the Rydberg (ndσ, ndσ′ ← (3a′′/13a)), n ≥ 3 members of the Rydberg (ndπ′(a′) ← (3a′′/13a)) and n = 3 members of the Rydberg (npσ′ ← (10a′/12a)) transitions. The experimental absolute photoabsorption cross sections have subsequently been used to calculate the photolysis lifetime of ethanol in the Earth's atmosphere (0–50 km), showing that solar photolysis is expected to be a weak sink at altitudes lower than 40 km to ●OH radical reactions. Potential energy curves for the lowest-lying excited electronic states, as a function of the O–H and the C–OH coordinates, are also obtained employing the equation of motion coupled cluster single and doubles (EOM-CCSD) and time dependant density functional theory (TD-DFT) methods. These show clear dissociation character at inter-nuclear distances greater than 2.0 Å for the RO–H and 2.2 Å for the RC–OH bond lengths, indicating the rather complex multidimensional character of the potential energy surfaces involved.

Investigations into the gas-phase photolysis and OH radical kinetics of nitrocatechols: implications of intramolecular interactions on their atmospheric behaviour

Abstract. The Environmental Simulation Chamber made of Quartz from the University “Alexandru Ioan Cuza” (ESC-Q-UAIC), at Iasi, Romania, was used to investigate the gas-phase reaction rate coefficients for four nitrocatechols toward OH radicals under simulated atmospheric conditions. Employing relative rate techniques at a temperature of 298 ± 2 K and a total air pressure of 1 atm, the obtained rate coefficients (in 10−12 cm3 s−1) were as follows: k3NCAT = (3.41 ± 0.37) for 3-nitrocatechol and k5M3NCAT = (5.55 ± 0.45) for 5-methyl-3-nitrocatechol at 365 nm, using CH3ONO photolysis as OH radicals source and dimethyl ether and cyclohexane as reference compounds, and k4NCAT = (1.27 ± 0.19) for 4-nitrocatechol and k4M5NCAT = (0.92 ± 0.14) for 4-methyl-5-nitrocatechol at 254 nm using H2O2 as OH radicals source and dimethyl ether and methanol as reference compounds. The photolysis rates in the actinic region, scaled to atmospheric relevant conditions by NO2 photolysis, were evaluated for 3-nitrocatechol and 5-methyl-3-nitrocatechol: J3NCAT = (3.06 ± 0.16) × 10−4 s−1 and J5M3NCAT = (2.14 ± 0.18) × 10−4 s−1, respectively. The photolysis rate constants at 254 nm were measured for 4-nitrocatechol and 4-methyl-5-nitrocatechol and the obtained values are J4NCAT = (6.7 ± 0.1) × 10−5 s−1 and J4M5NCAT = (3.2 ± 0.3) × 10−5 s−1. Considering the obtained results, our study suggests that photolysis may be the main degradation process for 3-nitrocatechol and 5-methyl-3-nitrocatechol in the atmosphere, with a photolytic lifetime in the atmosphere of up to 2 h. Results are discussed in terms of the reactivity of the four nitrocatechols under investigation toward OH-radical-initiated oxidation and their structural features. The rate coefficient values of the nitrocatechols are also compared with those estimated from the structure-activity relationship for monocyclic aromatic hydrocarbons and assessed in relation to their gas-phase IR spectra. Additional comparison with similar compounds is also presented, underlining the implications toward possible degradation pathways and atmospheric behaviour.

A combined experimental and theoretical study of the lowest-lying valence, Rydberg and ionic electronic states of 2,4,6-trichloroanisole

We investigate for the first time the gas-phase lowest-lying valence, Rydberg and ionic electronic states of 2,4,6-trichloroanisole (TCA) using synchrotron radiation for photoabsorption and photoelectron spectroscopy. The high-resolution vacuum ultraviolet photoabsorption spectrum, in the 4.0–10.8 eV energy-range, has been measured with absolute photoabsorption cross-sections and, thanks to novel ab initio calculations of the vertical energies and oscillator strengths, an assignment of the electronic transitions is comprehensively reported. The assignment of weak vibrational features in the absorption bands of TCA reveal that the ring and C–Cl stretching modes are mainly active. In the photoelectron spectrum the lowest 18 ionic bands, between 8 and 30 eV, have been observed and assigned using the first set of calculated valence and outer valence vertical ionisation energies. Finally, the measured absolute photoabsorption cross sections have also been used to estimate the photolysis lifetime of TCA in the upper stratosphere (20–50 km).

Absolute Photoabsorption Cross-Sections of Methanol for Terrestrial and Astrophysical Relevance.

We investigate the methanol absorption spectrum in the range 5.5-10.8 eV to provide accurate and absolute cross-sections values. The main goal of this study is to provide a comprehensive analysis of methanol electronic-state spectroscopy by employing high-resolution vacuum ultraviolet (VUV) photoabsorption measurements together with state-of-the-art quantum chemical calculation methods. The VUV spectrum reveals several new features that are not previously reported in literature, for n > 3 in the transitions (nsσ(a') ← (2a″)) (1A' ← X̃1A') and (nsσ, npσ, npσ', ndσ ← (7a')) (1A' ← X̃1A'), and with particular relevance to vibrational progressions of the CH3 rocking mode, v11'(a″), mode in the (3pπ(a″) ← (2a″)) (21A' ← X̃1A') absorption band at 8.318 eV. The measured absolute photoabsorption cross-sections have subsequently been used to calculate the photolysis lifetime of methanol in the Earth's atmosphere from the ground level up to the limit of the stratosphere (50 km altitude). This shows that solar photolysis plays a negligible role in the removal of methanol from the lower atmosphere compared with competing sink mechanisms. Torsional potential energy scans, as a function of the internal rotation angle for the ground and first Rydberg states, have also been calculated as part of this investigation.

Laboratory Insights into the Diel Cycle of Optical and Chemical Transformations of Biomass Burning Brown Carbon Aerosols.

Transformations of biomass burning brown carbon aerosols (BB-BrC) over their diurnal lifecycle are currently not well studied. In this study, the aging of BB tar proxy aerosols processed by NO3• under dark conditions followed by the photochemical OH• reaction and photolysis were investigated in tandem flow reactors. The results show that O3 oxidation in the dark diminishes light absorption of wood tar aerosols, resulting in higher particle single-scattering albedo (SSA). NO3• reactions augment the mass absorption coefficient (MAC) of the aerosols by a factor of 2–3 by forming secondary chromophores, such as nitroaromatic compounds (NACs) and organonitrates. Subsequent OH• oxidation and direct photolysis both decompose the organic nitrates (ONs, representing bulk functionalities of NACs and organonitrates) in the NO3•-aged wood tar aerosols, thus decreasing particle absorption. Moreover, NACs degrade faster than organonitrates by photochemical aging. The NO3•-aged wood tar aerosols are more susceptible to photolysis than to OH• reactions. The photolysis lifetimes for the ONs and for the absorbance of the NO3•-aged aerosols are on the order of hours under typical solar irradiation, while the absorption and ON lifetimes toward OH• oxidation are substantially longer. Overall, nighttime aging via NO3• reactions increases the light absorption of wood tar aerosols and shortens their absorption lifetime under daytime conditions.

On the electronic structure of methyl butyrate and methyl valerate

We present novel results of the analysis of the electronic structure of two aliphatic esters: methyl butyrate and methyl valerate. High-resolution photoabsorption spectra were collected and analyzed over the energy range 4.0–10.8 eV and showed for both the molecules not only a clear band of the HOMO to LUMO transition, but also vibronic structure associated with the first Rydberg-valence transition. Photoelectron spectra recorded from 9 to over 28 eV revealed many ionization states with the first adiabatic ionization energies found to be 9.977 eV and 9.959 eV for methyl butyrate and methyl valerate, respectively. Ab initio calculations have been performed in order to help assign the photoabsorption and photoelectron features. Photolysis life times in the atmosphere were calculated revealing that photolysis is not competitive over hydroxyl radical scavenging in the process of removal of these esters from the atmosphere.Graphical abstract

The electronic excited states of dichloromethane in the 5.8-10.8 eV energy range investigated by experimental and theoretical methods

We present a comprehensive experimental high-resolution vacuum ultraviolet (VUV) photoabsorption spectrum of dichloromethane, CH2Cl2, with absolute cross sections determined for the full 5.8–10.8 eV energy-range. The calculations on the vertical excitation energies and oscillator strengths were performed using the equation-of-motion coupled cluster method, restricted to the single and double excitations level (EOM-CCSD), and were used to help analyse the valence and Rydberg structures in the photoabsorption spectrum. The present spectrum additionally reveals several new features not previously reported in the literature, with particular reference to the valence σCCl*(10a1)←nCl(7b2)(11B2←X˜1A1)and (σCCl*(10a1)←nCl(9a1)+σCH*(11a1)←nCl(7b2))(11A1←X˜1A1)transitions at 7.519 and 7.793 eV. A vibrational progression of the CCl2 symmetric stretching, ν3′, and CCl2scissoring, v4′(a1), modes have also been assigned for the first time in the 7.4–8.6 eV energy range. The measured absolute photoabsorption cross sections have been used to calculate the photolysis lifetime of dichloromethane in the Earth's atmosphere (0–50 km). Potential energy curves as a function of the C–Cl coordinate, for the four lowest-lying excited A′ and A″ electronic states, have additionally been calculated at the EOM-CCSD level of theory.

Human odour thresholds are tuned to atmospheric chemical lifetimes.

In this study, the odour thresholds (OT) and atmospheric lifetimes (AL) were compared for a suite of volatile organic compounds. It was found that odour threshold, as determined by the triangle bag method, correlated surprisingly well with atmospheric lifetime for a given chemical family. Molecules with short atmospheric lifetimes with respect to the primary atmospheric oxidant OH tend to be more sensitively detected by the human nose. Overall the correlation of odour threshold with atmospheric lifetime was better than with mass and vapour pressure. Several outliers from the correlations for particular chemical families were examined in detail. For example, diacetyl was an outlier in the ketone dataset that fitted the trend when its more important photolysis lifetime was included; and similarly, the relatively low odour threshold of carbonyl sulfide (OCS) was interpreted in terms of uptake by vegetation. The OT/AL relationship suggests that OH rate constants can be used as a first-order estimate for odour thresholds (and vice versa). We speculate that the nose's high sensitivity to chemicals that are reactive in the air is likely an evolved rather than a learned condition. This is based on the lack of dependence on ozone in the aliphatics, that the anthropogenically emitted aromatic compounds had the worst correlation, and that OCS had a much lower than predicted OT. Finally, we use the OT/AL relationships derived to predict odour thresholds and rate constants that have not yet been determined in order to provide a test to this hypothesis.This article is part of the Theo Murphy meeting issue ‘Olfactory communication in humans’.