Characterisation of urban and remote atmospheres using comprehensive two dimensional gas chromatography

Volatile organic compounds (VOCs) are key precursors to ozone and particulate matter, two of the most important air pollutants. Air quality interventions have successfully reduced the release of short chain VOCs in urban areas. The increased use of diesel vehicles has created an increase in the direct emission of longer chain VOCs. However, these compounds are not considered as part of air quality strategies and there are few atmospheric measurements of them to date. This thesis details continuous measurements of VOCs in London, a developed megacity, using comprehensive two dimensional gas chromatography. Analysis of this large suite of VOC measurements have shown that the higher carbon number species emitted from diesel vehicles can dominate gas phase reactive carbon in cities with a significant diesel fleet. Comparison of these real-world observations with emissions inventories has highlighted that there is a significant under prediction of the emissions of higher carbon number species. This presents a considerable policy challenge; the focus must now switch to VOCs released from diesel as this vehicle type is increasingly replacing gasoline world-wide. Further analysis of the London data has provided evidence of both anthropogenic and biogenic emission sources. The measurement of the higher carbon number species has allowed for OH reactivity to be more accurately modelled. Detailed analysis of the ethanol observations provided direct evidence that the use of bio-ethanol blended gasoline in the UK is having an impact on the composition of the atmosphere. The combination of heart-cut and comprehensive two dimensional gas chromatography into a single instrument has made the measurement of both small and large chain VOCs possible. This instrument compares well to existing instrumentation and when deployed to a rural location (Bachok, Malaysia) provided hourly time-resolved measurements of C5-C13 VOCs

Unexpectedly high concentrations of monoterpenes in a study of UK homes

The abundance of volatile organic compounds (VOCs) found in homes depends on many factors such as emissions, ventilation and the oxidative environment and these are evolving over time, reflecting changes in chemical use, behaviour and building design/materials. The concentrations of VOCs in 25 UK homes of varying ages, design and occupancy were quantified using continuous indoor air sampling over five days. Air was collected through low flow (1 mL min-1) constant flow restrictors into evacuated 6 L internally silica-treated canisters until the canisters reached atmospheric pressure. This was followed by thermal desorption-gas chromatography and high mass accuracy time-of-flight mass spectrometry (TD-GC-TOF/MS). A fully quantitative analysis was performed on the eight most abundant hydrocarbon-based VOCs found. Despite differences in building characteristics and occupant numbers 94% of the homes had d-limonene or α-pinene as the most abundant VOCs. The variability seen across the 25 homes in concentrations of monoterpenes indoors was considerably greater than that of species such as isoprene, benzene, toluene and xylenes. The variance in VOCs indoors appeared to be strongly influenced by occupant activities such as cleaning with 5-day average concentrations of d-limonene ranging from 18 μg m-3 to over 1400 μg m-3, a peak domestic value that is possibly the highest yet reported in the literature

Variability of polycyclic aromatic hydrocarbons and their oxidative derivatives in wintertime Beijing, China

Ambient particulate matter (PM) can contain a mix of different toxic species derived from a wide variety of sources. This study quantifies the diurnal variation and nocturnal abundance of 16 polycyclic aromatic hydrocarbons (PAHs), 10 oxygenated PAHs (OPAHs) and 9 nitrated PAHs (NPAHs) in ambient PM in central Beijing during winter. Target compounds were identified and quantified using gas chromatography-time-of-flight mass spectrometry (GC-Q-ToF-MS). The total concentration of PAHs varied between 18 and 297 ngm-3 over 3 h daytime filter samples and from 23 to 165 ngm-3 in 15 h night-time samples. The total concentrations of PAHs over 24 h varied between 37 and 180 ngm-3 (mean: 97±43 ngm-3). The total daytime concentrations during high particulate loading conditions for PAHs, OPAHs and NPAHs were 224, 54 and 2.3 ngm-3, respectively. The most abundant PAHs were fluoranthene (33 ngm-3), chrysene (27 ngm-3), pyrene (27 ngm-3), benzo[a]pyrene (27 ngm-3), benzo[b]fluoranthene (25 ngm-3), benzo[a]anthracene (20 ngm-3) and phenanthrene (18 ngm-3). The most abundant OPAHs were 9,10-anthraquinone (18 ngm-3), 1,8-naphthalic anhydride (14 ngm-3) and 9-fluorenone (12 ngm-3), and the three most abundant NPAHs were 9-nitroanthracene (0.84 ngm-3), 3-nitrofluoranthene (0.78 ngm-3) and 3-nitrodibenzofuran (0.45 ngm-3). Σ PAHs and Σ OPAHs showed a strong positive correlation with the gas-phase abundance of NO, CO, SO2 and HONO, indicating that PAHs and OPAHs can be associated with both local and regional emissions. Diagnostic ratios suggested emissions from traffic road and coal combustion were the predominant sources of PAHs in Beijing and also revealed the main source of NPAHs to be secondary photochemical formation rather than primary emissions. PM2.5 and NPAHs showed a strong correlation with gas-phase HONO. 9- Nitroanthracene appeared to undergo a photodegradation during the daytime and showed a strong positive correlation with ambient HONO (R D 0:90, P <0:001). The lifetime excess lung cancer risk for those species that have available toxicological data (16 PAHs, 1 OPAH and 6 NPAHs) was calculated to be in the range 10-5 to 10-3 (risk per million people ranges from 26 to 2053 cases per year)

A self-consistent, multi-variate method for the determination of gas phase rate coefficients, applied to reactions of atmospheric VOCs and the hydroxyl radical

Gas-phase rate coefficients are fundamental to understanding atmospheric chemistry, yet experimental data are not available for the oxidation reactions of many of the thousands of volatile organic compounds (VOCs) observed in the troposphere. Here a new experimental method is reported for the simultaneous study of reactions between multiple different VOCs and OH, the most important daytime atmospheric radical oxidant. This technique is based upon established relative rate concepts but has the advantage of a much higher throughput of target VOCs. By evaluating multiple VOCs in each experiment, and through measurement of the depletion in each VOC after reaction with OH, the OH + VOC reaction rate coefficients can be derived. Results from experiments conducted under controlled laboratory conditions were in good agreement with the available literature for the reaction of nineteen VOCs, prepared in synthetic gas mixtures, with OH. This approach was used to determine a rate coefficient for the reaction of OH with 2,3-dimethylpent-1-ene for the first time; k = 5.7 (±0.3) × 10–11–cm3 molecule−1 s−1. In addition, a further seven VOCs had only two, or fewer, individual OH rate coefficient measurements available in the literature. The results from this work were in good agreement with those measurements. A similar dataset, at an elevated temperature of 323 (±10) K, was used to determine new OH rate coefficients for twelve aromatic, five alkane, five alkene and three monoterpene VOC + OH reactions. In OH relative reactivity experiments that used ambient air at the University of York, a large number of different VOCs were observed, of which 23 were positively identified. 19 OH rate coefficients were derived from these ambient air samples, including ten reactions for which data was previously unavailable at the elevated reaction temperature of T = 323 (±10) K

Measurement of NOx fluxes from a tall tower in Beijing

Abstract relates to a poster presentation at the EGU 2017 General Assembly. Abstract is available via Official URL link

The Effect of Varying Engine Conditions on Unregulated VOC Diesel Exhaust Emissions

Abstract. An extensive set of measurements were performed to investigate the effect of different engine conditions (i.e. load, speed, temperature, "driving scenarios") and emission control devices (with/without diesel oxidative catalyst, DOC) on the composition and abundance of unregulated exhaust gas emissions from a light-duty diesel engine. Exhaust emissions were introduced into an atmospheric chamber and measured using thermal desorption comprehensive two-dimensional gas chromatography coupled to a flame ionisation detector (TD-GC×GC-FID). In total, 16 individual and 8 groups of volatile organic compounds (VOCs) were measured in the exhaust gas, ranging from volatile to intermediate volatility. The total speciated VOC (∑SpVOC) emission rates varied significantly with different engine conditions, ranging from 70 to 9268 milligrams of VOC mass per kilogram of fuel burnt (mg kg-1). ∑SpVOC emission rates generally decreased with increasing engine load and temperature, and to a lesser degree, engine speed. The exhaust gas composition changed as a result of two main influencing factors, the DOC hydrocarbon (HC) removal efficiency and engine combustion efficiency. Increased DOC HC removal efficiency and engine combustion efficiency resulted in a greater percentage contribution of the C7 to C12 branched aliphatics and C7 to C12 n-alkanes, respectively, to the ∑SpVOC emission rate. The investigated DOC removed 46 ± 10 % of the ∑SpVOC emissions, with removal efficiencies of 83 ± 3 % for the single-ring aromatics and 39 ± 12 % for the aliphatics (branched and straight-chain). The DOC aliphatic removal efficiency generally decreased with increasing carbon chain length. The emission factors of n-nonane to n-tridecane were compared with on-road diesel emissions from a highway tunnel in Oakland California. Comparable emission factors were from experiments with relatively high engine loads and speeds, engine conditions which are consistent with the driving conditions of the on-road diesel vehicles. Emission factors from low engine loads and speeds (e.g. cold-start) showed no agreement with the on-road diesel emissions as expected, with the emission factors observed to be 2 to 8 times greater. To our knowledge, this is the first study which has explicitly discussed the effect of the DOC HC removal efficiency and combustion efficiency on the exhaust gas composition. With further work, compositional differences in exhaust gas emissions as a function of engine temperature, could be implemented into air-quality models, resulting in improved refinement and better understanding of diesel exhaust emissions on local air quality. </jats:p

The air quality impacts of pre-operational hydraulic fracturing activities

Hydraulic fracturing (fracking) is a short phase in unconventional oil and natural gas (O&G) development. Before fracking there is a lengthy period of preparation, which can represent a significant proportion of the well lifecycle. Extensive infrastructure is delivered onto site, leading to increased volumes of heavy traffic, energy generation and construction work on site. Termed the “pre-operational” period, this is rarely investigated as air quality evaluations typically focus on the extraction phase. In this work we quantify the change in air pollution during pre-operational activities at a shale gas exploration site near Kirby Misperton, North Yorkshire, England. Baseline air quality measurements were made two years prior to any shale gas activity and were used as a training dataset for random forest (RF) machine learning models. The models allowed for a comparison between observed air quality during the pre-operational phase and a counterfactual business as usual (BAU) prediction. During the pre-operational phase a significant deviation from the BAU scenario was observed. This was characterised by significant enhancements in NOx and a concurrent reduction in O3, caused by extensive additional vehicle movements and the presence of combustion sources such as generators on the well pad. During the pre-operational period NOx increased by 274 % and O3 decreased by 29 % when compared to BAU model values. There was also an increase in primary emissions of NO2 during the pre-operational phase which may have implications for the attainment of ambient air quality standards in the local surroundings. Unconventional O&G development remains under discussion as a potential option for improving the security of supply of domestic energy, tensioned however against significant environmental impacts. Here we demonstrate that the preparative work needed to begin fracking elevates air pollution in its own right, a further potential disbenefit that should be considered

Seasonality of Formic Acid (HCOOH) in London during the ClearfLo Campaign

Following measurements in the winter of 2012, formic acid (HCOOH) and nitric acid (HNO3) were measured using a chemical ionization mass spectrometer (CIMS) during the Summer Clean Air for London (ClearfLo) campaign in London, 2012. Consequently, the seasonal dependence of formic acid sources could be better understood. A mean formic acid concentration of 1.3 ppb and a maximum of 12.7 ppb was measured which is significantly greater than that measured during the winter campaign (0.63 ppb and 6.7 ppb, respectively). Daily calibrations of formic acid during the summer campaign gave sensitivities of 1.2 ion counts s-1 parts per trillion (ppt) by volume-1 and a limit of detection of 34 ppt. During the summer campaign, there was no correlation between formic acid and anthropogenic emissions such as NOx and CO or peaks associated with the rush hour as was identified in the winter. Rather, peaks in formic acid were observed that correlated with solar irradiance. Analysis using a photochemical trajectory model has been conducted to determine the source of this formic acid. The contribution of formic acid formation through ozonolysis of alkenes is important but the secondary production from biogenic VOCs could be the most dominant source of formic acid at this measurement site during the summer

Sources of non-methane hydrocarbons in surface air in Delhi, India

Rapid economic growth and development have exacerbated air quality problems across India, driven by many poorly understood pollution sources and understanding their relative importance remains critical to characterising the key drivers of air pollution. A comprehensive suite of measurements of 90 non-methane hydrocarbons (NMHCs) (C2–C14), including 12 speciated monoterpenes and higher molecular weight monoaromatics, were made at an urban site in Old Delhi during the pre-monsoon (28-May to 05-Jun 2018) and post-monsoon (11 to 27-Oct 2018) seasons using dual-channel gas chromatography (DC-GC-FID) and two-dimensional gas chromatography (GC×GC-FID). Significantly higher mixing ratios of NMHCs were measured during the post-monsoon campaign, with a mean night-time enhancement of around 6. Like with NOx and CO, strong diurnal profiles were observed for all NMHCs, except isoprene, with very high NMHC mixing ratios between 35–1485 ppbv. The sum of mixing ratios of benzene, toluene, ethylbenzene and xylenes (BTEX) routinely exceeded 100 ppbv at night during the post-monsoon period, with a maximum measured mixing ratio of monoaromatic species of 370 ppbv. The mixing ratio of highly reactive monoterpenes peaked at around 6 ppbv in the post-monsoon campaign and correlated strongly with anthropogenic NMHCs, suggesting a strong non-biogenic source in Delhi. A detailed source apportionment study was conducted which included regression analysis to CO, acetylene and other NMHCs, hierarchical cluster analysis, EPA UNMIX 6.0, principal component analysis/absolute principal component scores (PCA/APCS) and comparison with NMHC ratios (benzene/toluene and i-/n-pentane) in ambient samples to liquid and solid fuels. These analyses suggested the primary source of anthropogenic NMHCs in Delhi was from traffic emissions (petrol and diesel), with average mixing ratio contributions from Unmix and PCA/APCS models of 38% from petrol, 14% from diesel and 32% from liquified petroleum gas (LPG) with a smaller contribution (16%) from solid fuel combustion. Detailed consideration of the underlying meteorology during the campaigns showed that the extreme night-time mixing ratios of NMHCs during the post-monsoon campaign were the result of emissions into a very shallow and stagnant boundary layer. The results of this study suggest that despite widespread open burning in India, traffic-related petrol and diesel emissions remain the key drivers of gas-phase urban air pollution in Delhi

Development of a combined heart-cut and comprehensive two-dimensional gas chromatography system to extend the carbon range of volatile organic compounds analysis in a single instrument

The majority of atmospheric measurements of volatile organic compounds (VOCs) are usually limited to a small range, either in volatility or time resolution. A combined heart-cut gas chromatography (GC) with comprehensive two-dimensional GC (GC×GC) instrument was developed, specifically to increase the number of VOCs analysed using a single instrument. The system uses valve based modulation and was fully automated, making it suitable for use in the field. A laboratory comparison to an existing dual-channel GC (DC-GC) instrument demonstrated that this new GC-GC×GC can accurately measure atmospheric mixing ratios of C -C VOC species with a wide range of functionalities. Approximately hourly field measurements were conducted at a remote marine atmospheric research station in Bachok, Malaysia. This region was shown to be influenced by clean marine air masses, local anthropogenic and biogenic emission sources and aged emissions transported from highly polluted South East Asian regions. A dramatic shift in air mass direction was observed each day associated with the development of a sea breeze, which influenced the diurnal profiles of species measured at the Bachok site. A proton-transfer-reaction mass spectrometer (PTR-MS) was also deployed at Bachok and compared to the new GC-GC×GC instrument. Overall, the GC-GC×GC instrument has been shown to perform well in lab comparisons and during field observations. This represents a good compromise between volatility and high complexity measurements of VOCs