Abstract. Measurements of mixing ratios and stable carbon isotope ratios of aromatic volatile organic compounds (VOC) in the atmosphere were made in Toronto (Canada) in 2009 and 2010. Consistent with the kinetic isotope effect for reactions of aromatic VOC with the OH radical the observed stable carbon isotope ratios are on average significantly heavier than the isotope ratios of their emissions. The change of carbon isotope ratio between emission and observation is used to determine the extent of photochemical processing (photochemical age,  ∫ [OH]dt) of the different VOC. It is found that  ∫ [OH]dt of different VOC depends strongly on the VOC reactivity. This demonstrates that for this set of observations the assumption of a uniform  ∫ [OH]dt for VOC with different reactivity is not justified and that the observed values for  ∫ [OH]dt are the result of mixing of VOC from air masses with different values for  ∫ [OH]dt. Based on comparison between carbon isotope ratios and VOC concentration ratios it is also found that the varying influence of sources with different VOC emission ratios has a larger impact on VOC concentration ratios than photochemical processing. It is concluded that for this data set the use of VOC concentration ratios to determine  ∫ [OH]dt would result in values for  ∫ [OH]dt inconsistent with carbon isotope ratios and that the concept of a uniform  ∫ [OH]dt for an air mass has to be replaced by the concept of individual values of an average  ∫ [OH]dt for VOC with different reactivity.

Abstract.A method for the determination of the stable carbon isotopic composition of atmospheric nitrophenols in the gas and particulate phases is presented. It has been proposed to use the combination of concentration and isotope ratio measurements of precursor and product to test the applicability of results of laboratory studies to the atmosphere. Nitrophenols are suspected to be secondary products formed specifically from the photooxidation of volatile organic compounds. XAD-4 TM resin was used as an adsorbent on quartz filters to sample ambient phenols using conventional high volume air samplers at York University in Toronto, Canada. Filters were extracted in acetonitrile, with a HPLC (high-performance liquid chromatography) clean-up step and a solid phase extraction step prior to derivatization with BSTFA (bis(trimethylsilyl) trifluoroacetamide). Concentration measurements were done with gas chromatographymass spectrometry and gas chromatography-isotope ratio mass spectrometry was used for isotope ratio analysis.The technique presented allows for atmospheric compound-specific isotopic composition measurements for five semi-volatile phenols with an estimated accuracy of 0.3-0.5 ‰ at atmospheric concentrations exceeding 0.1 ng m −3 while the detection limits for concentration measurements are in the pg m −3 range. Isotopic fractionation throughout the entire extraction procedure and analysis was proven to be below the precision of the isotope ratio measurements. The method was tested by conducting ambient measurements from September to December 2011.

Samples (633) of final coffee products were drawn from the markets of different European countries relative to the market share of each product type and brand. These samples were analysed in a cooperative action with nine different laboratories. With low limits of detection (mean detection limit approximately 0.5 ng/g) no OTA was found in over half of the samples (334 negatives). In the remaining samples occurrence of OTA at a rather low level was seen. Only four samples (all instants) exceeded a level of 10 ng/g, whereas for both instants, and roast and grounds (R & G), over three-quarters of the samples were in the range from nondetectable to 1 ng/g. The overall mean for all R & Gs was 0.8 ng/g and for all instant 1.3 ng/g (for samples in which no OTA was detected, half of the detection limit was included in this calculation). In the brewing methods frequently used in Europe the OTA is essentially fully extracted. Consumption of four cups of coffee per day (approximately 24 g R & G or approximately 8 g instant coffee) contributes on average 19 or 10 ng/day respectively. Four cups/day is above the per caput consumption level in most European contries. Compared with the Provisional Tolerable Weekly Intake (PTWI) recently set by the Joint FAO/WHO Expert Committee on Food Additives at 100 ng/kg bodyweight/week, consumption of 28 cups/week contributes up to 2% to the PTWI.

Abstract.A technique for the measurement of the stable isotope ratio of methylnitrophenols in atmospheric particulate matter is presented. Atmospheric samples from rural and suburban areas were collected for evaluation of the procedure. Particulate matter was collected on quartz fibre filters using dichotomous high volume air samplers. Methylnitrophenols were extracted from the filters using acetonitrile. The sample was then purified using a combination of high-performance liquid chromatography and solid phase extraction. The final solution was then divided into two aliquots. To one aliquot, a derivatising agent, Bis(trimethylsilyl)trifluoroacetamide, was added for Gas Chromatography-Mass Spectrometry analysis. The second half of the sample was stored in a refrigerator. For samples with concentrations exceeding 1 ng µl −1 , the second half of the sample was used for measurement of stable carbon isotope ratios by Gas Chromatography-Isotope Ratio Mass Spectrometry.The procedure described in this paper provides a method for the analysis of methylnitrophenols in atmospheric particulate matter at concentrations as low as 0.3 pg m −3 and for stable isotope ratios with an accuracy of better than ±0.5 ‰ for concentrations exceeding 100 pg m −3 .In all atmospheric particulate matter samples analysed, 2-methyl-4-nitrophenol was found to be the most abundant methylnitrophenol, with concentrations ranging from the low pg m −3 range in rural areas to more than 200 pg m −3 in some samples from a suburban location.

The dependence of ozone formation on the mixing ratios of volatile organic compounds (VOCs) and nitrogen oxides (NO x ) has been widely studied. In addition to the atmospheric levels of VOCs and NO x , the extent of photochemical processing of VOCs has a strong impact on ozone levels. Although methods for measuring atmospheric mixing ratios of VOCs and NO x are well established and results of those measurements are widely available, determination of the extent of photochemical processing of VOCs, known as photochemical age (PCA), is difficult. In this article a recently developed methodology for the determination of PCA for individual compounds based on the change in their stable carbon isotope composition is used to investigate the dependence between ozone and VOC or NO x mixing ratios at a rural site in Ontario, Canada, during fall and winter. The results show that under these conditions the variability in VOC mixing ratios is predominantly a result of the varying impact of local emissions and not a result of changes in the extent of atmospheric processing. This explains why the mixing ratio of ozone shows no systematic dependence on the mixing ratios of VOCs or NO x in this environment and at this time of the year. RÉSUMÉ [Traduit par la rédaction] La dépendance de la formation de l'ozone à l'égard des rapports de mélange des composés organiques volatiles (COV) et des oxydes d'azote (NO x ) a fait l'objet de nombreuses études. En plus des concentrations atmosphériques de COV et de NO x , le degré d'avancement du traitement photochimique des COV a un effet marqué sur les concentrations d'ozone. Même si les méthodes de mesure des rapports de mélange atmosphérique des COV et des NO x sont bien établies et que les résultats de ces mesures sont facilement disponibles, il reste difficile de déterminer le degré d'avancement du traitement photochimique des COV, que l'on nomme « âge photochimique ». Dans cet article, nous employons une méthodologie récemment mise au point pour la détermination de l'âge photochimique de différents composés, basée sur le changement dans la composition de leurs isotopes stables du carbone, pour étudier la dépendance de l'ozone à l'égard des rapports de mélange des COV ou des NO x à un site rural en Ontario, au Canada, durant l'automne et l'hiver. Les résultats montrent que dans ces conditions la variabilité dans les rapports de mélange des COV est principalement attribuable à l'effet variable des émissions locales et non à des changements dans le degré d'avancement du traitement atmosphérique. Cela explique pourquoi le rapport de mélange de l'ozone n'affiche pas de dépendance systématique à l'égard des rapports de mélange des COV ou des NO x dans cet environnement et à ce moment de l'année.