The impact of biogenic, anthropogenic, and biomass burning volatile organic compound emissions on regional and seasonal variations in secondary organic aerosol

The global secondary organic aerosol (SOA) budget is highly uncertain, with global annual SOA production rates, estimated from global models, ranging over an order of magnitude and simulated SOA concentrations underestimated compared to observations. In this study, we use a global composition-climate model (UKCA) with interactive chemistry and aerosol microphysics to provide an in-depth analysis of the impact of each VOC source on the global SOA budget and its seasonality. We further quantify the role of each source on SOA spatial distributions, and evaluate simulated seasonal SOA concentrations against a comprehensive set of observations. The annual global SOA production rates from monoterpene, isoprene, biomass burning, and anthropogenic precursor sources is 19.9, 19.6, 9.5, and 24.6Tg (SOA) a-1, respectively. When all sources are included, the SOA production rate from all sources is 73.6Tg (SOA) a-1, which lies within the range of estimates from previous modelling studies. SOA production rates and SOA burdens from biogenic and biomass burning SOA sources peak during Northern Hemisphere (NH) summer. In contrast, the anthropogenic SOA production rate is fairly constant all year round. However, the global anthropogenic SOA burden does have a seasonal cycle which is lowest during NH summer, which is probably due to enhanced wet removal. Inclusion of the new SOA sources also accelerates the ageing by condensation of primary organic aerosol (POA), making it more hydrophilic, leading to a reduction in the POA lifetime. With monoterpene as the only source of SOA, simulated SOA and total organic aerosol (OA) concentrations are underestimated by the model when compared to surface and aircraft measurements. Model agreement with observations improves with all new sources added, primarily due to the inclusion of the anthropogenic source of SOA, although a negative bias remains. A further sensitivity simulation was performed with an increased anthropogenic SOA reaction yield, corresponding to an annual global SOA production rate of 70.0Tg (SOA) a-1. Whilst simulated SOA concentrations improved relative to observations, they were still underestimated in urban environments and overestimated further downwind and in remote environments. In contrast, the inclusion of SOA from isoprene and biomass burning did not improve model-observations biases substantially except at one out of two tropical locations. However, these findings may reflect the very limited availability of observations to evaluate the model, which are primarily located in the NH mid-latitudes where anthropogenic emissions are high. Our results highlight that, within the current uncertainty limits in SOA sources and reaction yields, over the NH mid-latitudes, a large anthropogenic SOA source results in good agreement with observations. However, more observations are needed to establish the importance of biomass burning and biogenic sources of SOA in model agreement with observations.</p

Influence of Mid-Latitude Cyclones on European Background Surface Ozone Investigated in Observations, MACC and MERRA-2 Reanalyses

The relationship between springtime mid-latitude cyclones and background ozone at two rural monitoring sites on the west coast of Europe -- Mace Head, Ireland and Monte Velho, Portugal -- is explored using a combination of observations and three reanalyses: 1) the European Centre for Medium-Range Weather Forecasts' (ECMWF) ERA-Interim reanalysis, 2) the Monitoring Atmospheric Composition and Climate (MACC) reanalysis and 3) NASA's Modern-Era Retrospective Analysis for Research and Applications Version-2 (MERRA-2) reanalysis. The ERA-Interim cyclone tracks are used here to establish the long-term relationship between cyclones and ozone observations (since 1988). The MACC reanalysis data set, which covers the period 2003-2012, is produced with the ECMWF integrated forecast system (IFS) model two-way coupled to a chemistry transport model (CTM). Since the MACC reanalysis uses a similar atmospheric model to ERA-Interim, MACC is used to explore the mechanisms within the case study cyclones that can influence surface ozone concentrations at Mace Head and Monte Velho. The MERRA-2 reanalysis also provides 3D distributions of ozone, although less ideal for analysis of surface ozone concentrations since MERRA-2 ozone under represents ozone variability outside the stratosphere as it does not have a detailed chemistry scheme or emission sources for the troposphere. The MERRA-2 reanalysis, which has the potential to identify more features within the cyclones as the resolution is higher than the MACC reanalysis, is used in conjunction with the MACC reanalysis to provide a measure of uncertainty to the case study analysis. We found the main source of high ozone to these two sites is from the stratosphere, which is well represented in both the MERRA-2 and the MACC reanalyses, either from direct injection into the cyclone or associated with aged airstreams from decaying downstream cyclones that can become entrained and descend toward the surface within new cyclones over the NA region

Measurement error in time-series analysis: a simulation study comparing modelled and monitored data

Background: Assessing health effects from background exposure to air pollution is often hampered by the sparseness of pollution monitoring networks. However, regional atmospheric chemistry-transport models (CTMs) can provide pollution data with national coverage at fine geographical and temporal resolution. We used statistical simulation to compare the impact on epidemiological time-series analysis of additive measurement error in sparse monitor data as opposed to geographically and temporally complete model data. Methods: Statistical simulations were based on a theoretical area of 4 regions each consisting of twenty-five 5 km × 5 km grid-squares. In the context of a 3-year Poisson regression time-series analysis of the association between mortality and a single pollutant, we compared the error impact of using daily grid-specific model data as opposed to daily regional average monitor data. We investigated how this comparison was affected if we changed the number of grids per region containing a monitor. To inform simulations, estimates (e.g. of pollutant means) were obtained from observed monitor data for 2003–2006 for national network sites across the UK and corresponding model data that were generated by the EMEP-WRF CTM. Average within-site correlations between observed monitor and model data were 0.73 and 0.76 for rural and urban daily maximum 8-hour ozone respectively, and 0.67 and 0.61 for rural and urban loge(daily 1-hour maximum NO2). Results: When regional averages were based on 5 or 10 monitors per region, health effect estimates exhibited little bias. However, with only 1 monitor per region, the regression coefficient in our time-series analysis was attenuated by an estimated 6% for urban background ozone, 13% for rural ozone, 29% for urban background loge(NO2) and 38% for rural loge(NO2). For grid-specific model data the corresponding figures were 19%, 22%, 54% and 44% respectively, i.e. similar for rural loge(NO2) but more marked for urban loge(NO2). Conclusion: Even if correlations between model and monitor data appear reasonably strong, additive classical measurement error in model data may lead to appreciable bias in health effect estimates. As process-based air pollution models become more widely used in epidemiological time-series analysis, assessments of error impact that include statistical simulation may be useful

Process-based modelling of NH3 exchange with grazed grasslands

In this study the GAG model, a process-based ammonia (NH3) emission model for urine patches, was extended and applied for the field scale. The new model (GAG_field) was tested over two modelling periods, for which micrometeorological NH3 flux data were available. Acknowledging uncertainties in the measurements, the model was able to simulate the main features of the observed fluxes. The temporal evolution of the simulated NH3 exchange flux was found to be dominated by NH3 emission from the urine patches, offset by simultaneous NH3 deposition to areas of the field not affected by urine. The simulations show how NH3 fluxes over a grazed field in a given day can be affected by urine patches deposited several days earlier, linked to the interaction of volatilization processes with soil pH dynamics. Sensitivity analysis showed that GAG_field was more sensitive to soil buffering capacity (β), field capacity (θfc) and permanent wilting point (θpwp) than the patch-scale model. The reason for these different sensitivities is dual. Firstly, the difference originates from the different scales. Secondly, the difference can be explained by the different initial soil pH and physical properties, which determine the maximum volume of urine that can be stored in the NH3 source layer. It was found that in the case of urine patches with a higher initial soil pH and higher initial soil water content, the sensitivity of NH3 exchange to β was stronger. Also, in the case of a higher initial soil water content, NH3 exchange was more sensitive to the changes in θfc and θpwp. The sensitivity analysis showed that the nitrogen content of urine (cN) is associated with high uncertainty in the simulated fluxes. However, model experiments based on cN values randomized from an estimated statistical distribution indicated that this uncertainty is considerably smaller in practice

Infrared spectroscopy of HII regions and starburst galaxies

This thesis is concerned with testing models of the infrared Hel 2.058^m/Br7 ratio as a function of effective temperature in HII regions. This ratio is known to be sensitive to effective temperatures in the range Te //=32-38,000K. Near-infrared observational data from ultracompact (UC) HII regions, compact HII regions and giant HII regions or the nuclei of starburst galaxies is presented and analysed for this purpose.Observations of UCHII regions show that HII region models with an electron densities of ne = 104cm-3, electron temperatures in the range Te=5,000-10,000K and a Galactic helium abundance can reproduce the observed Hel 2.058 /im/Br7 ratios in these objects, subject to one condition. As the electron temperature is increased from Te=5,000K, microturbulence is incorporated into the model which counteracts the increase in the Hel 2.058 /¿m/Br7 ratio with electron temperature. Microturbulent velocities of the order ~20kms_1 are required at Te=10,000K, in agreement with observed radio recombination line and high resolution Hel and HI measurements.Lower Hel 2.058/xm/Br7 ratios are generally found in larger objects classed as com­pact HII regions, consistent with lower electron densities or lower stellar effective tem­peratures, or a combination of both effects in such objects. Alternative electron densities have been calculated from radio continuum measurements and provide evidence to sug­gest that electron densities are slightly lower in most of the compact HII regions than in the UCHII regions.Detailed density gradient modelling of the Hel 2.058/rm/Br7 ratio has been per­formed, which reveals the need for realistic density distributions and explicit integration over the volume of the source when attempting to model specific HII regions. Accurate integrated electron densities or density gradients act as an alternative to microturbu­lence to bring theoretical Ilel 2.058/xm/Br7 ratios into agreement with observations for electron temperature models higher than Te=5,000K.Finally, a large sample of starburst galaxies ale analysed. The Hel 2.058 /xm/Br7 ratios are much lower than found in compact or UCHII regions consistent with the proposal that the integrated Hel 2.058¿mr/Br7 emission is generally dominated by low density giant HII regions present in these galaxies. Effective temperatures derived from the Hel 2.058/rm/Bry ratio are consistent with those estimated from FIR fine structure lines. From consideration of new models of the Hel 2.058¿¿m/Bry ratio, the combination of optical HeI/H/3 data with Hel 2.058 /¿m/Bry observations extends the sensitivity of these model ratios to a wider range of effective temperatures

Atypical attention and autism spectrum disorders (ASD) symptoms: Development and interactions with learning and memory

This thesis investigates the nature of atypical attention in relation to autism spectrum disorders (ASD) symptoms, as well as the mechanisms by which it may relate to social impairment. First, does atypical non-social attention predict social impairment over time in the context of ASD, suggestive of a causal relationship? Second, if atypical attention plays a role in social impairments in ASD, what is the mechanism? With regards to the first question, longitudinal data with children at familial risk for ASD demonstrated a unidirectional relationship between non-social attention and social functioning at the cognitive level: 2-year-old non-social attention predicted 3- year-old face recognition, but there was no relationship between 2-year-old face popout and 3-year-old visual search. Additionally, we examined the relationships between ASD and ADHD symptoms over three years in children at high risk for both—children with fragile X syndrome. This allowed for investigating atypical non-social attention and social impairment at the symptoms level, again revealing a unidirectional relationship with ADHD symptoms predicting ASD symptoms over time but not the reverse. These findings suggest that atypical non-social attention may contribute to social impairment. With regards to the second question, a novel eye-tracking and visual search paradigm revealed how task irrelevant social stimuli in natural scenes can lead to poorer subsequent explicit spatial contextual memory and altered memory-guided attention orienting—effects that were moderated by autistic traits and social anxiety within a neurotypical population. Further, this research found cross-sectional development, comparing 6-10-year-old children to young adults, and investigated the neural markers of social stimuli's effect on memory. These studies suggest a possible mechanism whereby a reduced social attention bias could lead autistic individuals to learn and remember less about people and the social world and result in social impairment

Tropospheric Ozone Assessment Report : Present-day ozone distribution and trends relevant to human health

This study quantifies the present-day global and regional distributions (2010–2014) and trends (2000–2014) for five ozone metrics relevant for short-term and long-term human exposure. These metrics, calculated by the Tropospheric Ozone Assessment Report, are: 4th highest daily maximum 8-hour ozone (4MDA8); number of days with MDA8 > 70 ppb (NDGT70), SOMO35 (annual Sum of Ozone Means Over 35 ppb) and two seasonally averaged metrics (3MMDA1; AVGMDA8). These metrics were explored at ozone monitoring sites worldwide, which were classified as urban or non-urban based on population and nighttime lights data.Present-day distributions of 4MDA8 and NDGT70, determined predominantly by peak values, are similar with highest levels in western North America, southern Europe and East Asia. For the other three metrics, distributions are similar with North–South gradients more prominent across Europe and Japan. Between 2000 and 2014, significant negative trends in 4MDA8 and NDGT70 occur at most US and some European sites. In contrast, significant positive trends are found at many sites in South Korea and Hong Kong, with mixed trends across Japan. The other three metrics have similar, negative trends for many non-urban North American and some European and Japanese sites, and positive trends across much of East Asia. Globally, metrics at many sites exhibit non-significant trends. At 59% of all sites there is a common direction and significance in the trend across all five metrics, whilst 4MDA8 and NDGT70 have a common trend at ~80% of all sites. Sensitivity analysis shows AVGMDA8 trends differ with averaging period (warm season or annual). Trends are unchanged at many sites when a 1995–2014 period is used; although fewer sites exhibit non-significant trends. Over the longer period 1970–2014, most Japanese sites exhibit positive 4MDA8/SOMO35 trends. Insufficient data exist to characterize ozone trends for the rest of Asia and other world regions

Future global mortality from changes in air pollution attributable to climate change

Ground-level ozone and fine particulate matter (PM2.5) are associated with premature human mortality1-4; their future concentrations depend on changes in emissions, which dominate the near-term5, and on climate change6,7. Previous global studies of the air quality-related health effects of future climate change8,9 used single atmospheric models. However, in related studies, mortality results differ among models10-12. Here we use an ensemble of global chemistry-climate models13 to show that premature mortality from changes in air pollution attributable to climate change, under the high greenhouse gas scenario RCP8.514, is likely positive. We estimate 3,340 (-30,300 to 47,100) ozone-related deaths in 2030, relative to 2000 climate, and 43,600 (-195,000 to 237,000) in 2100 (14% of the increase in global ozone-related mortality). For PM2.5, we estimate 55,600 (-34,300 to 164,000) deaths in 2030 and 215,000 (-76,100 to 595,000) in 2100 (countering by 16% the global decrease in PM2.5-related mortality). Premature mortality attributable to climate change is estimated to be positive in all regions except Africa, and is greatest in India and East Asia. Most individual models yield increased mortality from climate change, but some yield decreases, suggesting caution in interpreting results from a single model. Climate change mitigation will likely reduce air pollution-related mortality

Using image-reflections to support undergraduate students’ relational employability: A practitioner reflection

This practitioner reflection explores our integration of the Relational Employability Framework within the Health Research Project capstone unit of a Bachelor of Health Science degree. To address the historically low quality of student reflections, we incorporated image-based reflective activities to improve engagement and depth. These activities encouraged students to use visual media to examine their developing relational employability. We developed and implemented a series of tutorial activities designed to scaffold this process, aiming to foster deeper reflective practice and highlight its importance for career development and employability. Our reflections indicate that, while grades did not significantly increase, students showed enhanced critical thinking and engagement with reflective practice, suggesting the framework’s effectiveness in broadening awareness and enriching employability overall. We discuss the need for peer support among educators to sustain and enhance reflective practices in teaching-learning and conclude with thoughts on our ongoing efforts to embed and expand reflective practices in teaching approaches