Search

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 (m=n-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 370 nm to 0.94–0.96 at 950 nm 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 370 nm and 0.002–0.003 at 950 nm. 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 660–950 nm 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.

Volatile organic compounds (VOCs) are important precursors to the formation of ozone (O3) and secondary organic aero-sols (SOA) and can also have direct human health impacts. Generally, given the range and number of VOC species, their emissions are poorly characterised. The VOC levels in Beijing during two campaigns (APHH) were investigated using a dispersion model (NAME), and a chemical box model (AtChem2) in order to understand how chemistry and transport affect the VOC concentrations in Beijing. Emissions of VOCs in Beijing and contributions from outside Beijing were modelled using the NAME dispersion model combined with the emission inventories and were used to initialize the AtChem2 box model. The modelled concentrations of VOCs from the NAME-AtChem2 combination were then compared to the output of a chemical transport model (GEOS-Chem). The results from the emission inventories and the NAME air mass pathways suggest that industrial sources to the south of Beijing and within Beijing both in summer and winter are very important in con-trolling the VOC levels in Beijing. A number of scenarios with different nitrogen oxides to ozone ratios (NOx / O3) and hydroxyl (OH) levels were simulated to determine the changes in VOC levels. In Beijing over 80 % of VOC are emitted locally during winter, while during summer about 35 % of VOC concentrations (greater for some individual species) are transported into Beijing from the surrounding regions. Most winter scenarios are in good agreement with daily GEOS-Chem simulations, with the best agreements seen for the modelled concentrations of ethanol, benzene and propane with correlation coefficients of 0.67, 0.63 and 0.64 respectively. Furthermore, the production of formaldehyde within 24 hours air travel from Beijing was investigated, and it was determined that 90 % of formaldehyde in the winter and 83 % in the summer in Beijing is secondary, produced from oxidation of non-methane volatile organic compounds (NMVOCs). The benzene / CO and toluene / CO ratios during the campaign is very similar to the ratio derived from literature for 2014 in Beijing, however more data are needed to enable investigation of more species over longer timeframes to determine whether this ratio can be applied to predicting VOCs in Beijing. The results suggest that VOC concentrations in Beijing are driven predominantly by sources within Beijing and by local atmospheric chemistry during the winter, and by a combination of transport and chemistry during the summer. Moreover, the relationship of the NOx / VOC and O3 during winter and summer shows the need for season-specific policy measures.

Strict seasonal emission controls are a popular measure in China for addressing severe air pollution, in particular fine particulate matter (PM2.5). Here we evaluate the efficacy of these measures, with a particular focus on the strict emission controls imposed on pollution sources in 28 cities in and around the Beijing-Tianjin-Hebei region (BTH) in autumn-winter 2017/2018. For this we use the GEOS-Chem chemical transport model and air pollutant measurements from the national and Beijing local monitoring networks, after evaluating the network data with independent measurements and correcting large biases in the bottom-up emissions inventory. The network measurements are temporally consistent (r > 0.9 for PM2.5 and r > 0.7 for gases) with the independent measurements, though with systematic differences of 5–17 % for nitrogen dioxide (NO2) and 16–28 % for carbon monoxide (CO). The average decrease in monitoring network PM2.5 in BTH in autumn-winter 2017/2018 relative to the previous year is 27 %, declining from 103 to 75 µg m−3. The regional decline in PM2.5 in the model is 20 %, exceeding the regional target of 15 %. According to the model, pollution control measures led to decline in PM2.5 precursor emissions of 0.27 Tg NOx (as NO), 0.66 Tg sulfur dioxide (SO2), 70 Gg organic carbon (OC), and 50 Gg black carbon (BC). We find though that these alone only lead to an 8 % decline in PM2.5 and that interannual variability in meteorology accounts for more than half (57 %) the decline. This demonstrates that year-on-year comparisons are misleading for assessing the efficacy of air pollution measures and should be taken into consideration when extending such measures beyond BTH.

Air pollution in megacities represents one of the greatest environmental challenges. Our observed results show that the dramatic NOx decrease (77%) led to significant O3 increases (a factor of 2) during the COVID‐19 lockdown in megacity Hangzhou, China. Model simulations further demonstrate large increases of daytime OH and HO2 radicals and nighttime NO3 radical, which can promote the gas‐phase reaction and nocturnal multiphase chemistry. Therefore, enhanced NO3 − and SO4 2− formation was observed during the COVID‐19 lockdown because of the enhanced oxidizing capacity. The PM2.5 decrease was only partially offset by enhanced aerosol formation with its reduction reaching 50%. In particular, NO3 − decreased largely by 68%. PM2.5 chemical analysis reveals that vehicular emissions mainly contributed to PM2.5 under normal conditions in Hangzhou. Whereas, stationary sources dominated the residual PM2.5 during the COVID‐19 lockdown. This study provides evidence that large reductions in vehicular emissions can effectively mitigate air pollution in megacities., Key Points Air pollutants PM10, PM2.5, NOx, CO, and SO2 decreased whereas O3 increased during the COVID‐19 lockdown in megacity HangzhouEnhanced NO3 − and SO4 2− formation caused by the enhanced oxidizing capacity partially offset the decrease of PM2.5 in megacity HangzhouThe contribution of vehicular emissions to PM2.5 was over stationary sources under normal conditions in megacity Hangzhou

True air quality improvements during the COVID-19 lockdowns in global cities are more limited than we thought., The COVID-19 lockdowns led to major reductions in air pollutant emissions. Here, we quantitatively evaluate changes in ambient NO2, O3, and PM2.5 concentrations arising from these emission changes in 11 cities globally by applying a deweathering machine learning technique. Sudden decreases in deweathered NO2 concentrations and increases in O3 were observed in almost all cities. However, the decline in NO2 concentrations attributable to the lockdowns was not as large as expected, at reductions of 10 to 50%. Accordingly, O3 increased by 2 to 30% (except for London), the total gaseous oxidant (Ox = NO2 + O3) showed limited change, and PM2.5 concentrations decreased in most cities studied but increased in London and Paris. Our results demonstrate the need for a sophisticated analysis to quantify air quality impacts of interventions and indicate that true air quality improvements were notably more limited than some earlier reports or observational data suggested.

Black carbon (BC) not only warms the atmosphere but also affects human health. The nationwide lockdown due to the Coronavirus Disease 2019 (COVID‐19) pandemic led to a major reduction in human activity during the past 30 years. Here, the concentration of BC in the urban, urban‐industry, suburb, and rural areas of a megacity Hangzhou were monitored using a multiwavelength Aethalometer to estimate the impact of the COVID‐19 lockdown on BC emissions. The citywide BC decreased by 44% from 2.30 to 1.29 μg/m3 following the COVID‐19 lockdown period. The source apportionment based on the Aethalometer model shows that vehicle emission reduction responded to BC decline in the urban area and biomass burning in rural areas around the megacity had a regional contribution of BC. We highlight that the emission controls of vehicles in urban areas and biomass burning in rural areas should be more efficient in reducing BC in the megacity Hangzhou., Key Points BC concentrations during the COVID‐lockdown were reduced by 44% in a megacity of ChinaBC from fossil fuels has the largest reduction in urban area during the COVID‐lockdownVehicles and industrial activities are the major contributors of BC in the megacity, followed by and biomass burning

Cemented tailings backfill (CTB), an evolutive granular medium, is utilized extensively in underground mines as a sustainable solution to tailings disposal and for ground control. To achieve full ore recovery, the backfill mass is often exposed to mine blasts during the extraction of ore pillars. Nevertheless, limitations in knowledge regarding the dynamic response of CTB and the lack of design standards to ensure backfill stability during blasting have caused numerous failure incidents of backfill systems. Therefore, the proposition to utilize reliable tools for a rational characterization of CTB behaviour under mine blasts has become imperative. However, current studies conducted to evaluate blast response of mine backfills are based on empirical equations and simple constitutive models, and the evolutive nature of CTB due to multiphysics processes occurring in the material has not yet been considered. Therefore, in this PhD study, a series of fundamental multiphysics models are developed to assess the blast response of CTB with ongoing cementation. Specifically, a novel coupled chemo-viscoplastic cap model is developed to characterize the rate-dependence, irrecoverable compaction, and nonlinear hydrostatic behaviour of CTB under blast loading. The evolution in the dynamic response of CTB due to binder hydration is incorporated in the model and quantified with a binder hydration model. Moreover, the performance of CTB is not only affected by the hydration of binders (chemical, C), but is also significantly influenced by the thermal (T), hydraulic (H), and mechanical (M) factors it is subjected to during its service life. Therefore, a new multiphysics-viscoplastic cap model is then developed to characterize the blast response of CTB under the impact of complex THMC processes of its curing stage. Furthermore, as a granular medium, the early-age CTB with no or negligible cementation is also subjected to the risk of blast-induced liquefaction. Thus, a new total-stress viscoplastic cap model is developed to account for the impedance of pore water and capture excess pore pressure development in early-age backfills during blast loading. The developed multiphysics models are validated against a series of experiments on both laboratory and field scales, and the effectiveness and predictive ability of the models are verified by good agreement between the simulated and measured results. Then, the validated models are applied to practical engineering issues pertaining to field backfilling operations. These include simulation of the blast wave propagation in field CTB structures and the blast-induced liquefaction susceptibility of early-age fill mass, as well as blast-induced stress redistribution in early-age fill mass. The different dynamic responses of CTB to varied backfilling conditions and design strategies are then scrutinized and analyzed. Thus, the research performed in this PhD study can provide useful tools and technical insight for a better understanding of the blast response of CTB as well as optimal design of CTB systems in such dynamic condition.