Interpreting changes in anthropogenic emissions underlying abrupt changes in observed air quality using surface and satellite observations and a chemical transport model

Effective air quality policy is hindered by inaccurate estimates of precursor emissions, unvalidated, sparse or absent monitoring networks, and uncertain formation pathways of air pollution. Of particular concern are regions with severe air pollution, such as northern China and, large cities in South and Southeast Asia, and large cities in the world with high anthropogenic emissions. This work makes use of field campaign measurements, reference network measurements, satellite observations and a chemical transport model (CTM) to address these knowledge gaps in these regions. In the Beijing-Tianjin-Hebei region (BTH) in northern China, the Chinese government implemented strict emission control measures in autumn-winter 2017/2018 to address fine particulate matter (PM2.5) pollution. PM2.5 reduction targets were met, so these controls are now adopted in other parts of China, even though the relative role of emission controls and meteorology was not assessed. Surface observations of air quality from monitoring networks (validated against field campaign measurements) and the GEOS-Chem CTM were used after addressing large biases in the regional bottom-up anthropogenic emission inventory for China. According to the model, emission controls accounted for less than half (at most 43%) the decline in total PM2.5 while most (57%) was due to interannual variability in meteorology. Specifically, a deeper planetary boundary layer, stronger winds, and lower relative humidity during the emission control period. Emission controls alone would not achieve the PM2.5 reduction targets of 15-25% in this region. Cities in South and Southeast Asia are developing rapidly, but routine, up-to-date and publicly available inventories of emissions are lacking for this region. Nitrogen oxides (NOx) emissions in cities are important precursors to health-hazardous PM2.5 and tropospheric ozone (O3) where it is a greenhouse gas. NOx lifetimes and emissions over 10 large cities in South and Southeast Asia in 2019 were obtained by applying an exponentially modified Gaussian (EMG) approach with a wind rotation technique to the nitrogen dioxide (NO2) tropospheric vertical column densities (VCDs) from the high spatial resolution TROPOspheric Monitoring Instrument (TROPOMI). Annual averaged NOx emissions range from 100 mol s-1 for Delhi, Dhaka and Singapore. This is comparable to the range of emissions estimates for polluted cities in China. Bottom-up NOx emissions from a widely used publicly available global inventory exceed the top-down estimates for most cities. The discrepancy is >100% for Chennai, Singapore and Jakarta. It was only possible to estimate top-down monthly NOx estimates for 3 cities, due to issues with the line density fitting parameters at these fine temporal scales. These ranged from 63 to 148 mol s-1 for Singapore (annual mean 114 mol s-1), 44 to 109 mol s-1 for Jakarta (68 mol s-1), and 26 to 67 mol s-1 for Manila (53 mol s-1). Month-to-month variability is absent in the bottom-up emission estimates. The discrepancies identified in this work need to be resolved to ensure the development of effective policies. Abrupt changes in air quality during COVID-19 lockdowns presented an opportunity to investigate changes in observed PM2.5, NOx and O3 pollution due to interventions. Surface observations of air quality in 11 cities worldwide were analysed. Observed NO2 decreased substantially at urban background and roadside sites in all the cities, by 10-60% at urban background sites, and by 29 53% at roadside sites. In contrast, observed O3 increased in all cities after the lockdowns, by 16-167% at urban background sites and by 20-156% at roadside sites. The percentage changes in observed PM2.5 are -39 to 153% at urban background sites, -41 to 108% at roadside sites, and -34 to 165% at rural sites. But by comparing observations in 2020 to those in 2016-2019 during the equivalent periods, results here demonstrated that the observations of air quality alone cannot represent the changes in emissions due to COVID-19 lockdowns as the impact of meteorology should be considered. Findings in this thesis demonstrate the application of observations from multiple platforms, innovative analytical techniques, and an advanced chemical transport model to abrupt changes in air quality in time and space to better understand air pollution precursor emissions and formation pathways and to interpret the relative contribution from changes in emissions and meteorology. Such information is vital for developing well-informed environmental policies

Diagnosing domestic and transboundary sources of fine particulate matter (PM2.5) in UK cities using GEOS-Chem

The UK is set to impose a stricter ambient annual mean fine particulate matter (PM2.5) standard than was first adopted fourteen years ago. This necessitates strengthened knowledge of the magnitude and sources that influence urban PM2.5 in UK cities to ensure compliance and improve public health. Here, we use a regional-scale chemical transport model (GEOS-Chem), validated with national ground-based observations, to quantify the influence of specific sources within and transported to the mid-sized UK city Leicester. Of the sources targeted, we find that agricultural emissions of ammonia (NH3) make the largest contribution (3.7 μg m−3 or 38 % of PM2.5) to annual mean PM2.5 in Leicester. Another important contributor is long-range transport of pollution from continental Europe accounting for 1.8 μg m−3 or 19 % of total annual mean PM2.5. City sources are a much smaller portion (0.2 μg m−3; 2 %). We also apply GEOS-Chem to the much larger cities Birmingham and London to find that agricultural emissions of NH3 have a greater influence than city sources for Birmingham (32 % agriculture, 19 % city) and London (25 % agriculture, 13 % city). The portion from continental Europe is 16 % for Birmingham and 28 % for London. Action plans aimed at national agricultural sources of NH3 and strengthened supranational agreements would be most effective at alleviating PM2.5 in most UK cities

Impact of Legislated and Best Available Emission Control Measures on UK Particulate Matter Pollution, Premature Mortality, and Nitrogen-Sensitive Habitats

Past emission controls in the UK have substantially reduced precursor emissions of health-hazardous fine particles (PM2.5) and nitrogen pollution detrimental to ecosystems. Still, 79% of the UK exceeds the World Health Organization (WHO) guideline for annual mean PM2.5 of 5 μg m-3 and there is no enforcement of controls on agricultural sources of ammonia (NH3). NH3 is a phytotoxin and an increasingly large contributor to PM2.5 and nitrogen deposited to sensitive habitats. Here we use emissions projections, the GEOS-Chem model, high-resolution data sets, and contemporary exposure-risk relationships to assess potential human and ecosystem health co-benefits in 2030 relative to the present day of adopting legislated or best available emission control measures. We estimate that present-day annual adult premature mortality attributable to exposure to PM2.5 is 48,625 (95% confidence interval: 45,188-52,595), that harmful amounts of reactive nitrogen deposit to almost all (95%) sensitive habitat areas, and that 75% of ambient NH3 exceeds levels safe for bryophytes and lichens. Legal measures decrease the extent of the UK above the WHO guideline to 58% and avoid 6,800 premature deaths by 2030. This improves with best available measures to 36% of the UK and 13,300 avoided deaths. Both legal and best available measures are insufficient at reducing the extent of damage of nitrogen pollution to sensitive habitats. Far more ambitious reductions in nitrogen emissions (>80%) than is achievable with best available measures (34%) are required to halve the amount of excess nitrogen deposited to sensitive habitats

Impact of legislated and best available emission control measures on UK particulate matter pollution, premature mortality, and nitrogen-sensitive habitats

Past emission controls in the UK have substantially reduced precursor emissions of health-hazardous fine particles (PM2.5) and nitrogen pollution detrimental to ecosystems. Still, 79% of the UK exceeds the World Health Organization (WHO) guideline for annual mean PM2.5 of 5 μg m−3 and there is no enforcement of controls on agricultural sources of ammonia (NH3). NH3 is a phytotoxin and an increasingly large contributor to PM2.5 and nitrogen deposited to sensitive habitats. Here we use emissions projections, the GEOS-Chem model, high-resolution data sets, and contemporary exposure-risk relationships to assess potential human and ecosystem health co-benefits in 2030 relative to the present day of adopting legislated or best available emission control measures. We estimate that present-day annual adult premature mortality attributable to exposure to PM2.5 is 48,625 (95% confidence interval: 45,188–52,595), that harmful amounts of reactive nitrogen deposit to almost all (95%) sensitive habitat areas, and that 75% of ambient NH3 exceeds levels safe for bryophytes and lichens. Legal measures decrease the extent of the UK above the WHO guideline to 58% and avoid 6,800 premature deaths by 2030. This improves with best available measures to 36% of the UK and 13,300 avoided deaths. Both legal and best available measures are insufficient at reducing the extent of damage of nitrogen pollution to sensitive habitats. Far more ambitious reductions in nitrogen emissions (>80%) than is achievable with best available measures (34%) are required to halve the amount of excess nitrogen deposited to sensitive habitats

Complex refractive index and single scattering albedo of Icelandic dust in the shortwave part of the spectrum

Icelandic dust can impact the radiative budget in high-latitude regions directly by affecting light absorption and scattering and indirectly by changing the surface albedo after dust deposition. This tends to produce a positive radiative forcing. However, the limited knowledge of the spectral optical properties of Icelandic dust prevents an accurate assessment of these radiative effects. Here, the spectral single scattering albedo (SSA) and the complex refractive index (mCombining double low linen-ik) of Icelandic dust from five major emission hotspots were retrieved between 370-950 nm using online measurements of size distribution and spectral absorption (βabs) and scattering (βsca) coefficients of particles suspended in a large-scale atmospheric simulation chamber. The SSA(λ) estimated from the measured βabs and βsca increased from 0.90-0.94 at 370nm to 0.94-0.96 at 950nm in Icelandic dust from the different hotspots, which falls within the range of mineral dust from northern Africa and eastern Asia. The spectral complex refractive index was retrieved by minimizing the differences between the measured βabs and βsca and those computed using the Mie theory for spherical and internally homogeneous particles, using the size distribution data as input. The real part of the complex refractive index (n(λ)) was found to be 1.60-1.61 in the different samples and be independent of wavelength. The imaginary part (k(λ)) was almost constant with wavelength and was found to be around 0.004 at 370nm and 0.002-0.003 at 950nm. The estimated complex refractive index was close to the initial estimates based on the mineralogical composition, also suggesting that the high magnetite content observed in Icelandic dust may contribute to its high absorption capacity in the shortwave part of the spectrum. The k(λ) values retrieved for Icelandic dust are at the upper end of the reported range for low-latitude dust (e.g., from the Sahel). Furthermore, Icelandic dust tends to be more absorbing towards the near-infrared. In Icelandic dust, k(λ) between 660-950nm was 2-8 times higher than most of the dust samples sourced in northern Africa and eastern Asia. This suggests that Icelandic dust may have a stronger positive direct radiative forcing on climate that has not been accounted for in climate predictions

A multiphysics-viscoplastic cap model for simulating blast response of cemented tailings backfill

Although a large number of previous researches have significantly contributed to the understanding of the quasi-static mechanical behavior of cemented tailings backfill, an evolutive porous medium used in underground mine cavities, very few efforts have been made to improve the knowledge on its response under sudden dynamic loading during the curing process. In fact, there is a great need for such information given that cemented backfill structures are often subjected to blast loadings due to mine exploitations. In this study, a coupled thermo-hydro-mechanical-chemical (THMC)-viscoplastic cap model is developed to describe the behavior of cementing mine backfill material under blast loading. A THMC model for cemented backfill is adopted to evaluate its behavior and evolution of its properties in curing processes with coupled thermal, hydraulic, mechanical and chemical factors. Then, the model is coupled to a Perzyna type of viscoplastic model with a modified smooth surface cap envelope and a variable bulk modulus, in order to reasonably capture the nonlinear and rate-dependent behaviors of the cemented tailings backfill under blast loading. All of the parameters required for the variable-modulus viscoplastic cap model were obtained by applying the THMC model to reproducing evolution of cemented paste backfill (CPB) properties in the curing process. Thus, the behavior of hydrating cemented backfill under high-rate impacts can be evaluated under any curing time of concern. The validation results of the proposed model indicate a good agreement between the experimental and the simulated results. The authors believe that the proposed model will contribute to a better understanding of the performance of hydrating cemented backfill under blasting, and also to practical risk management of backfill structures associated with such a dynamic condition

Study on the Accuracy of Fracture Criteria in Predicting Fracture Characteristics of Granite with Different Occurrence Depths

The fracture network of a deep geothermal reservoir forms the place for heat exchange between injected fluid and rock mass with high temperature. The fracture resistance ability of reservoir rocks will affect the formation of fracture-network structure, heat exchange and transmission characteristics, and reservoir mechanical stability. However, there are few reports on the fracture toughness and trajectory prediction of geothermal reservoirs with different depths. In this paper, the modified maximum tangential stress criterion (MMTS) is analyzed. The results show that the experimental data are significantly different from the theoretical estimate of MMTS under the influence of different occurrence depths. It is found that the fracture process zone (FPZ) seriously affects the accuracy of predicting fracture initiation angle and mixed-mode (I+II) fracture toughness by MMTS. The FPZ value, considering the influence of different occurrence depths, is modified, and the accuracy of MMTS in predicting the fracture mechanical characteristics of granite is improved. In addition, the mechanical test results show that the Brazilian splitting strength (σt) of granite fluctuates increase with the increase in temperature. With the increase in deviatoric stress, the Brazilian splitting strength and the Brazilian splitting modulus of rock show a trend of first increasing, then decreasing, and then increasing