Air Particulate Matter in Pollluted New Zealand Urban Environments: Sources, Patterns and Transport

<p>During the winters of 2010 and 2011, three intensive particulate matter (PM) monitoring campaigns were undertaken in Masterton, Alexandra and Nelson, New Zealand. The goal of these campaigns was, for the first time, to identify the sources and factors contributing to elevated PM concentrations on an hourly time-scale. In each location, hourly coarse (PM₁₀-₂.₅; particles with aerodynamic diameters 2.5 μm < d < 10 μm) and fine (PM₂.₅; particles with aerodynamic diameters < 2.5 μm) samples, PM₁₀ (particles with aerodynamic diameters < 10 μm, incorporating the coarse and fine fractions) concentrations and meteorological variables were collected from a number of sites. Using elemental concentrations determined from ion beam analysis and black carbon concentrations determined from light reflection for each hourly sample, PM sources and their contributions on an hourly time-scale were identified using positive matrix factorization (PMF). In Masterton, where two sampling sites were employed, PM₁₀ concentrations displayed distinct diurnal cycles, with peak concentrations occurring in the evening (7 pm–midnight) and in the morning (7–9 am). Four PM sources were identified (biomass burning, marine aerosol, crustal matter and vehicles) at each of the sites and biomass burning was identified as the most dominant source of PM₁₀ during both the evening and morning. One of the sites experienced consistently higher PM₁₀ concentrations and katabatic flows across Masterton were identified to be the main contributor to this phenomenon. In Alexandra and Nelson, three sampling sites on a horizontal transect (upwind, central and downwind of the general katabatic flow pathway) and a fourth site located centrally, but at a height of 26 m, were incorporated in a novel study design. Each of the sites in Alexandra and Nelson also showed diurnal patterns in PM₁₀ concentrations. The central site in Alexandra experienced consistently higher PM₁₀ concentrations and four PM₁₀ sources were identified at each of the sites (biomass burning, marine aerosol, vehicles and crustal matter). Biomass burning was identified as the main source of PM₁₀ throughout the day at each of the sites. The convergence of numerous katabatic flows was identified as the contributing factor to the elevated PM₁₀ concentrations measured at the central site. In Nelson, five PM sources were identified at each of the sites (biomass burning, vehicles, marine aerosol, shipping sulfate and crustal matter) and biomass burning was identified as the dominant source of PM₁₀ throughout the day. Katabatic flows were also identified to play an important role in PM₁₀ transport. Analyses of source-specific (wood combustion and vehicles) PM samples was also undertaken, and the results of these analyses are included in this thesis.</p>

Air Particulate Matter in Pollluted New Zealand Urban Environments: Sources, Patterns and Transport

<p>During the winters of 2010 and 2011, three intensive particulate matter (PM) monitoring campaigns were undertaken in Masterton, Alexandra and Nelson, New Zealand. The goal of these campaigns was, for the first time, to identify the sources and factors contributing to elevated PM concentrations on an hourly time-scale. In each location, hourly coarse (PM₁₀-₂.₅; particles with aerodynamic diameters 2.5 μm < d < 10 μm) and fine (PM₂.₅; particles with aerodynamic diameters < 2.5 μm) samples, PM₁₀ (particles with aerodynamic diameters < 10 μm, incorporating the coarse and fine fractions) concentrations and meteorological variables were collected from a number of sites. Using elemental concentrations determined from ion beam analysis and black carbon concentrations determined from light reflection for each hourly sample, PM sources and their contributions on an hourly time-scale were identified using positive matrix factorization (PMF). In Masterton, where two sampling sites were employed, PM₁₀ concentrations displayed distinct diurnal cycles, with peak concentrations occurring in the evening (7 pm–midnight) and in the morning (7–9 am). Four PM sources were identified (biomass burning, marine aerosol, crustal matter and vehicles) at each of the sites and biomass burning was identified as the most dominant source of PM₁₀ during both the evening and morning. One of the sites experienced consistently higher PM₁₀ concentrations and katabatic flows across Masterton were identified to be the main contributor to this phenomenon. In Alexandra and Nelson, three sampling sites on a horizontal transect (upwind, central and downwind of the general katabatic flow pathway) and a fourth site located centrally, but at a height of 26 m, were incorporated in a novel study design. Each of the sites in Alexandra and Nelson also showed diurnal patterns in PM₁₀ concentrations. The central site in Alexandra experienced consistently higher PM₁₀ concentrations and four PM₁₀ sources were identified at each of the sites (biomass burning, marine aerosol, vehicles and crustal matter). Biomass burning was identified as the main source of PM₁₀ throughout the day at each of the sites. The convergence of numerous katabatic flows was identified as the contributing factor to the elevated PM₁₀ concentrations measured at the central site. In Nelson, five PM sources were identified at each of the sites (biomass burning, vehicles, marine aerosol, shipping sulfate and crustal matter) and biomass burning was identified as the dominant source of PM₁₀ throughout the day. Katabatic flows were also identified to play an important role in PM₁₀ transport. Analyses of source-specific (wood combustion and vehicles) PM samples was also undertaken, and the results of these analyses are included in this thesis.</p>

Can katabatic winds directly force retreat of Greenland outlet glaciers? Hypothesis test on Helheim Glacier in Sermilik Fjord

Katabatic winds drive sea ice export from glaciated fjords across Greenland and other high latitude environments, but few studies have investigated the extent to which they also drive inflow of warm water and whether they have a direct impact on glaciers stability. Using ERA5 reanalysis data, verified by two local weather stations, we create a timeseries of katabatic winds across Sermilik Fjord in southeast Greenland. Using this along with hydrographic data, from 2009–2013, positioned across the fjord, we analyse changes in fjord circulation during individual katabatic flows. Changes in melange presence are analysed too, via the use of MODIS and Landsat-7 satellite imagery. We show that warm water influxes are associated with katabatic winds, and that the potential submarine melt rates vary up to four-fold, dependant on katabatic wind strength. Rapid retreat of Helheim Glacier occurred during strong downslope wind events which removed the ice melange, and so the well documented retreat of Helheim between 2001–2005 is predicted to be in part because of strong katabatic winds. Removal of the ice-melange led to a series of calving events, driven by a lack of buttressing and weakness propagation up the glacier causing a retreat of up to 1.5 km. In contrast to previous research in which katabatic winds were seen as having an indirect influence on glaciers, we report direct forcing on Helheim Glacier through episodes of retreat occurring in response to inflow of warm water masses and removal of proglacial ice melange after downslope wind events.

Stable boundary layer height on a gentle slope

&lt;p&gt;Height of the stable boundary layer (SBL) presents an important diagnostic used to describe the relevant processes governing the evolution and characteristics of SBL, and the extent to which the surface is communicating with the free atmosphere. &amp;#160;Here we investigate the SBL height over a gentle (1&amp;#176;) mesoscale slope on which relatively deep mid-latitude katabatic flows (with jet maxima between 20 and 50 m) develop during clear nights. We show that detecting the SBL top depends on the method used (Richardson number, flux- and anisotropy-profiles). The detected SBL depth, mostly deviates from the jet maximum height or the top of the near-surface inversion. The flat terrain formulations for the SBL height correlate well with the detected top of the SBL if instead of background stratification, near-surface stratification is used in their formulations, however, they mostly largely overestimate the SBL height. The difference to flat-terrain SBL is also shown through the dependence of size of the dominant eddy with height. In katabatic flows the eddy size is semi-constant with height throughout the SBL, whereas in flat terrain eddy size varies significantly with height.&lt;/p&gt;

Avalanches and micrometeorology driving mass and energy balance of the lowest perennial ice field of the Alps: a case study

The mass balance of very small glaciers is often governed by anomalous snow accumulation, winter precipitation being multiplied by snow redistribution processes (gravitationally or wind driven), or suppressed snow ablation driven by micrometeorological effects lowering net radiation and/or turbulent heat exchange. In this case study, we analysed the relative contribution of snow accumulation and ablation processes governing the long- and short-term mass balance of the lowest perennial ice field of the Alps, the Ice Chapel, located at 870 m a.s.l. in the Berchtesgaden National Park (Germany). This study emphasizes the importance of the local topographic setting for the survival of a perennial ice field located far below the climatic snow line. Although long-term mass balance measurements of the ice field surface showed a dramatic mass loss between 1973 and 2014, the ice field mass balance was rather stable between 2014 and 2017 and even showed a strong mass gain in 2017/2018 with an increase in surface height by 50 %–100 % relative to the ice field thickness. Measurements suggest that the winter mass balance clearly dominated the annual mass balance. At the Ice Chapel surface, 92 % of snow accumulation was gained by snow avalanching, thus clearly governing the 2017/2018 winter mass balance of the ice field with mean snow depths of 32 m at the end of the accumulation period. Avalanche deposition was amplified by preferential deposition of snowfall in the wind-sheltered rock face surrounding the ice field. Detailed micrometeorological measurements combined with a numerical analysis of the small-scale near-surface atmospheric flow field identified the micrometeorological processes driving the energy balance of the ice field. Measurements revealed a katabatic flow system draining down the ice field throughout the day, showing strong temporal and spatial dynamics. The spatial origin of the thermal flow system was shown to be of particular importance for the ice field surface energy balance. Numerical simulation indicates that deep katabatic flows, which developed at higher-elevation shaded areas of the rock face and drained down the ice field, enhance sensible heat exchange towards the ice field surface by enhancing turbulence close to the ice surface. Conversely, the shallow katabatic flow developing at the ice field surface appeared to laterally decouple the local near-surface atmosphere from the warmer adjacent air suppressing heat exchange. Numerical results thus suggest that shallow katabatic flows driven by the cooling effect of the ice field surface are especially efficient in lowering the climatic sensitivity of the ice field to the surrounding rising air temperatures. Such micrometeorological phenomena must be taken into account when calculating mass and energy balances of very small glaciers or perennial ice fields at elevations far below the climatic snow line.

Avalanches and micrometeorology driving mass and energy balance of the lowest perennial ice field of the Alps: a case study

The mass balance of very small glaciers is often governed either by anomalous snow accumulation, winter precipitation being multiplied by snow redistribution processes (gravitationally or wind-driven), or by suppressed snow ablation driven by micrometeorological effects lowering net radiation and/or turbulent heat exchange. In this case study, we analysed the relative contribution of snow accumulation and ablation processes governing the long- and short-term mass balance of the lowest perennial ice field of the Alps, the Ice Chapel, located at 870 m ASL in the Berchtesgaden National Park (Germany). This study emphasizes the importance of the local topographic setting for the survival of a perennial ice field located far below the climatic snow line. Although long-term mass balance measurements of the ice field surface showed a dramatic mass loss between 1973 and 2014, the ice field mass balance was rather stable between 2014 and 2017 and even showed a strong mass gain in 2017/2018 with an increase in surface height by 50–100 % relative to the ice field thickness. Measurements suggest that the winter mass balance clearly dominated the annual mass balance with 3000 % of winter snow accumulation compared to a near-by flat field station. At the Ice Chapel surface, 92 % of snow accumulation was gained by snow avalanching, thus clearly governing the 2017/2018 winter mass balance of the ice field with mean snow depths of 32 m at the end of the accumulation period. Avalanche deposition was amplified by preferential deposition of snowfall in the wind-sheltered rock face surrounding the ice field. Detailed micrometeorological measurements combined with a numerical analysis of the small-scale near-surface atmospheric flow field identified the micrometeorological processes driving the energy balance of the ice field. Measurements revealed a katabatic flow system draining down the ice field throughout the day, showing strong temporal and spatial dynamics. The spatial origin of the onset of the thermal flow system, was shown to be of particular importance for the ice field surface energy balance. Deep katabatic flows, that developed at higher-elevated shaded areas of the rock face and drained down the ice field appeared to enhance sensible heat exchange towards the ice field surface by enhancing turbulence close to the ice surface. Contrary, the shallow katabatic flow developing at the ice field surface appeared to laterally decouple the local near-surface atmosphere from the warmer adjacent air supressing heat exchange. Results thus suggest that shallow katabatic flows driven by the cooling effect of the ice field surface are especially efficient in lowering the climatic sensitivity of the ice field to the surrounding rising air temperatures. Such micrometeorological phenomena must be taken into account when calculating mass and energy balances of very small glaciers or perennial ice fields at elevations far below the climatic snow line.

Weak and intense katabatic winds: impacts on turbulent characteristics in the stable boundary layer and CO₂ transport

The role of thermally-driven local downslope or katabatic flows in the dynamics and turbulent features of the stable boundary layer (SBL) is investigated using observations. Measurements are carried out in a relatively flat area 2-km away from the steep slopes of the Guadarrama Mountain Range (Spain). Forty katabatic events are selected from an observational database spanning the 2017-summer period, by using an objective and systematic algorithm that is able to account for local and synoptic forcings. We subsequently classify the katabatic events into weak, moderate and intense according to the observed maximum wind speed. This classification enables us to contrast the main differences in dynamics and thermal structure. We find that the stronger katabatic events are associated with an earlier onset time of these flows. We relate it to very low soil-moisture values (