Investigating the Formation of Organic Nitrogen Species during the Atmospheric Oxidation of Volatile Organic Compounds

Particulate matter less than 2.5 µm in diameter, termed PM2.5, lies within the respirable size range for humans and is therefore considered an important air quality standard. Within the respirable and often toxic chemical constituents in PM2.5 exist a range of organic nitrogen (ON) compounds. Atmospheric ON is difficult to characterize due to its various complexities; it spans a wide range of volatilities and polarities and originates from both biogenic and anthropogenic sources. This thesis details the use of two-dimensional gas chromatography (GC×GC) coupled to nitrogen chemiluminescence detection (NCD) for the analysis of ON compounds in atmospheric aerosol. The development of a highly sensitive analytical technique, relying on GC×GC-NCD, allowed for time-resolved measurements of carcinogenic nitrosamines in urban ambient PM2.5 to be made. The total nitrosamine concentrations in London exceeded the public health recommendations, prompting an estimation of the lifetime cancer risk from exposure to nitrosamines via inhalation to be made. The GC×GC-NCD technique was also used to investigate the formation of carcinogenic nitrosamines and nitramines formed during the atmospheric degradation of amines relevant to CO2 capture. Implementation of amine-based CO2 capture technology results in small but significant amounts of amines being emitted to the atmosphere. The atmospheric photo-oxidation pathways of various amines were investigated during a series of chamber experiments at the European Photoreactor. Complementary techniques such as ion chromatography (IC) were also used, to monitor the formation of aminium nitrate salts for example. Later work in this thesis includes the use of IC to characterise water-soluble ions in aerosol on the East coast of Peninsular Malaysia, and to study the influence of highly industrialised regions on aerosol composition at rural coastal locations. Additionally, GC×GC coupled to time-of-flight mass spectrometry (TOF-MS) was used as part of a collaborative project focusing on the composition of gas and particle phase cooking emissions

Post-Dieselgate : Evidence of NOx Emission Reductions Using On-Road Remote Sensing

The Dieselgate scandal which broke in September 2015 demonstrated that vehicle manufacturers, such as the Volkswagen Group (VWG), engaged in software-based manipulation which led to vehicles passing laboratory-based emission testing limits but were far more polluting while being driven on roads. Using 23 000 on-road remote sensing measurements of light-duty Euro 5 diesel vehicles in the United Kingdom between 2012 and 2018, VWG vehicles with the "Dieselgate-affected" EA189 engine demonstrated anomalous NOx emission behavior between the pre- and post-Dieselgate periods which was not observed in other vehicle makes or models. These anomalous changes can be explained by voluntary VWG hardware and software fixes which have led to improved NOx emission control. The VGW 1.6 L vehicles, with a simple hardware fix and a software upgrade, resulted in a 36% reduction in NOx, whereas the 2.0 L vehicles that required a software-only fix showed a 30% reduction in NOx once controlled for ambient temperature effects. These results show that even minor changes or upgrades can considerably reduce NOx emissions, which has implications for future emission control activities and local air quality

Underestimated Ammonia Emissions from Road Vehicles

In this study, we use comprehensive vehicle emission remote sensing measurements of over 230,000 passenger cars to estimate total UK ammonia (NH3) emissions. Estimates are made using "top-down"and "bottom-up"methods that demonstrate good agreement to within 1.1% for total fuel consumed or CO2 emitted. A central component of this study is the comprehensive nature of the bottom-up emission estimates that combine highly detailed remote sensing emission data with over 4000 km of 1 Hz real driving data. Total annual UK NH3 emissions from gasoline passenger cars are estimated to be 7.8 ± 0.3 kt from the bottom-up estimate compared with 3.0 ± 1.7 kt reported by the UK national inventory. An important conclusion from the analysis is that both methodologies confirm that gasoline passenger car NH3 emissions are underestimated by a factor of about 2.6 compared with the 2018 UK National Atmospheric Emissions Inventory. Furthermore, we find that inventory estimates of urban emissions of NH3 for passenger cars are underestimated by a factor of 17

Characterisation of ammonia emissions from gasoline and gasoline hybrid passenger cars

Recent evidence suggests NH3 emissions from road vehicles play an important role in the formation of fine particulate matter, especially in urban areas. However, there is little data available for NH3 emitted from road vehicles under real driving conditions, in part due to its lack of regulation in vehicle emission legislation. In this study, we use 210,000 vehicle emission remote sensing measurements to evaluate the complex mix of factors affecting NH3 emissions from gasoline and gasoline hybrid passenger cars. The influence of vehicle model year and manufacturer on NH3 emissions is considered, as well as the effect of vehicle deterioration. It is found that the amount of NH3 emitted increases as vehicle mileage increases. A comparison of cold start and hot exhaust NH3 emissions reveals that on average, cold start emissions are a factor of 1.7 times higher. New NH3 emission factors are developed, in addition to speed-emission curves that are potentially useful for national inventories. A new application of remote sensing data is reported, whereby the proportion of failed CO2 measurements for hybrid vehicles provides unique insight into the real world battery use of both conventional hybrid electric and plug-in hybrid electric vehicles, which is used to refine the NH3 emission factors for these vehicles

Strong Temperature Dependence for Light-Duty Diesel Vehicle NOx Emissions

Diesel-powered road vehicles are important sources for nitrogen oxide (NOx) emissions, and the European passenger fleet is highly dieselised, which has resulted in many European roadside environments being noncompliant with legal air quality standards for nitrogen dioxide (NO2). On the basis of vehicle emission remote sensing data for 300000 light-duty vehicles across the United Kingdom, light-duty diesel NOx emissions were found to be highly dependent on ambient temperature with low temperatures resulting in higher NOx emissions, i.e., a "low temperature NOx emission penalty" was identified. This feature was not observed for gasoline-powered vehicles. Older Euro 3 to 5 diesel vehicles emitted NOx similarly, but vehicles compliant with the latest Euro 6 emission standard emitted less NOx than older vehicles and demonstrated less of an ambient temperature dependence. This ambient temperature dependence is overlooked in current emission inventories but is of importance from an air quality perspective. Owing to Europe's climate, a predicted average of 38% more NOx emissions have burdened Europe when compared to temperatures encountered in laboratory test cycles. However, owing to the progressive elimination of vehicles demonstrating the most severe low temperature NOx penalty, light-duty diesel NOx emissions are likely to decrease more rapidly throughout Europe than currently thought

Verification of a National Emission Inventory and Influence of On-road Vehicle Manufacturer-Level Emissions

Road vehicles make important contributions to a wide range of pollutant emissions from the street level to global scales. The quantification of emissions from road vehicles is, however, highly challenging given the number of individual sources involved and the myriad factors that influence emissions such as fuel type, emission standard, and driving behavior. In this work, we use highly detailed and comprehensive vehicle emission remote sensing measurements made under real driving conditions to develop new bottom-up inventories that can be compared to official national inventory totals. We find that the total UK passenger car and light-duty van emissions of nitrogen oxides (NOx) are underestimated by 24-32%, and up to 47% in urban areas, compared with the UK national inventory, despite agreement within 1.5% for total fuel used. Emissions of NOx at a country level are also shown to vary considerably depending on the mix of vehicle manufacturers in the fleet. Adopting the on-road mix of vehicle manufacturers for six European countries results in up to a 13.4% range in total emissions of NOx. Accounting for the manufacturer-specific fleets at a country level could have a significant impact on emission estimates of NOx and other pollutants across the European countries, which are not currently reflected in emission inventories

The diminishing importance of nitrogen dioxide emissions from road vehicle exhaust

The direct emission of nitrogen dioxide (NO2) from road vehicle exhaust has been an important contributor to near-road ambient concentrations of NO2 in many European cities. Diesel vehicles and their use of emission control technologies such as Diesel Oxidation Catalysts, have dominated the emission of NO2 from road vehicles. In this work, we summarise findings from recent vehicle emission remote sensing measurements in the UK that provide detailed information on the emissions of NO2 and total NOx(NO2 + NO). We show that while new diesel cars and light commercial vehicles are associated with high (typically 30%) proportions of NO2/NOx, the amount of absolute NOx and NO2 emitted by most Euro 6 vehicles has decreased substantially and that absolute emissions of NO2 have been reducing since around 2007. Additionally, we find that the amount of NO2 decreases as the vehicle mileage increases. Taken together, these factors have led to substantial reductions in emissions of NO2 in recent years from light duty diesel vehicles, which has contributed to reduced roadside NO2 concentrations. There is a need however for commonly used emission factor models to account for these changes in emissions of NO2

Atmospheric Chemistry of tert-butylamine and AMP

The atmospheric chemistry of (CH3)3CNH2 (tert-butylamine, tBA) and (CH3)2(CH2OH)CNH2 (2-amino-2-methyl-1-propanol, AMP) has been studied by quantum chemistry methods and in photo-oxidation experiments in the EUPHORE chamber in Valencia (Spain). Aerosol formation and composition has been quantified. Yields of nitramines and other products in the photo-oxidations have been determined and complete photo-oxidation schemes including branching between the major reaction routes have been obtained. Published by Elsevier Ltd

Estimated Exposure Risks from Carcinogenic Nitrosamines in Urban Airborne Particulate Matter

Organic nitrogen (ON) compounds are present in atmospheric particulate matter (PM), but compared to their inorganic, hydrocarbon and oxygenated counterparts, they are difficult to characterize due to their complex chemical composition. Nitrosamines are a class of ON compounds known to be highly carcinogenic, and include species formed from nicotine degradation, but there are no detailed estimates of their abundance in ambient air. We use a highly sensitive analytical method, which is capable of separating over 700 ON compounds, to determine daily variability in nicotine, and 8 non specific and 4 tobacco specific nitrosamines in ambient PM from central London over two periods in winter and summer. The average total nitrosamine concentration was 5.2 ng m-3, substantially exceeding a current public recommendation of 0.3 ng m-3 on a daily basis. The lifetime cancer risk from nitrosamines in urban PM exceeded the U.S. Environmental Protection Agency guideline of 1 excess cancer cases per 1 million population exposed after 1 hour of exposure to observed concentrations per day over the duration of an adult lifetime. A clear relationship between ambient nitrosamines and total PM2.5 was observed with 1.2 ng m-3 ± 2.6 ng m-3 (total nitrosamine) per 10 µg m-3 PM2.5

Gasoline and diesel passenger car emissions deterioration using on-road emission measurements and measured mileage

Modern gasoline and diesel vehicles are equipped with highly effective emission control systems that result in low emissions of pollutants such as nitrogen oxides (NOx) when new. However, with increasing age or mileage, the emissions performance of vehicles can deteriorate over time, leading to increased emissions. In this work we use comprehensive vehicle emission remote sensing measurements collected over a wide range of conditions, together with individual vehicle measured mileage to quantify vehicle emissions deterioration. A quantile regression modelling approach is used to provide a more complete understanding of the distribution of deterioration effects that is not captured by considering mean changes over time. The approach accounts for factors such as driving conditions and ambient temperature, as well as determining whether deterioration affects whole populations of vehicles or a smaller subset of them. Accounting for these factors, we find that for most pollutants the rate of deterioration of emissions from pre-Euro 5 gasoline passenger cars is highly skewed. Between 5% and 10% of pre-Euro 5 gasoline passenger cars have emissions similar to a Euro 5 diesel car, suggesting that policies should be developed to accelerate their removal from the fleet. Furthermore, we find evidence that there are differences between vehicle manufacturers in the way emissions of NOx deteriorate