• 9 Pages
  • Published On: 07-10-2023

8.0 Background

In this concluding chapter, the key summary based on the objectives set for the study is described. The contribution of this thesis along with itswith principalmain findings are summarized and linked across in the previous chapter. The primemain limitations of this study arewere also described. Additionally, the important direction to the future work was discussed for this chapter.

8.1 Aims of this study

This study has successfully developed the state-of-arts methods for assessing an exposure to combustion-related air pollutant within indoor and outdoor settings. From the experiments and analyses performed, the objectives of this study were achieved as follows:

  • The innovative sampling and analysis techniques were developed using a low power sampler for PM, BC, NO₂ and pPAHs. The combination of portable, simple and relatively low-cost approacheses coupled with advanced real-time sensors were demonstrated for the collection system against the reference methods. The use of personal and environmental air monitors from relatively straightforward colour analysis of particle darkness, inexpensive passive samplers of NO₂ and sophisticated portable real-time monitors were established, thus making the assessment to these pollutants simpler. The complex and expensive analytical laboratory techniques using GC-MS for PAHs compounds were also described.
  • The identified cost-effective and low power monitors from the developed monitoring and analysis techniques were applied in the field evaluation of PM, BC and NO₂ concentrations. The simple methods for non-destructive and low-cost optical analysis of sequentially loaded filter air samples can be used to estimate BC from filter reflectance and scanned image calibrated against co-located micro-aethalometer observations. The real-time MicroAeth and Aeroqual sensors proved to be practical in this study for BC and NO₂ measurements.
  • The combustion related air pollutant metrics, including PM, BC and NO₂ within indoor and urban outdoor settings were assessed. The indoor PM, BC and NO₂ concentrations measured in the university offices were generally low compared to the outdoor pollution criteria specified in the UK National Air Quality Strategy and associated EU directives. There were consistently increased PM₂.₅ mass and BC concentrations, closer to the height of traffic exhaust emissions in the urban environment. The NO₂ concentrations measured in the urban Glasgow central had were exceeded the guideline value.
  • PM, BC and NO₂ concentrations within different settings and personal exposures were contrasted. The general contrasts were showing variability between these air pollutant concentrations captured by mobile and static measurements in the indoor and outdoor environments. The pattern of indoor combustion related to air pollutants exposure was influenced by supply and infiltration of outdoor concentrations through natural ventilation system in the office building. Meanwhile, children may have greater exposure than adults to airborne particles close to the urban roadsides. Commuters were exposed to high BC and NO₂ levels when walking along the urban street canyon zone. Marked elevations of BC and NO₂ concentrations were also observed for individual exposure from the proximity to traffic and industrial fracking equipment sources.
  • PM, BC and NO₂ were identified to be a useful proxy for combustion related air pollutants from urban traffic and diesel exhaust emissions. The results obtained from different area and personal level assessment of exposure of these air pollutant components were are found corrrelated against each other, however their absolute values may differ corresponding to the drivers of disparities such as sources from different settings, spatial and temporal variability.

8.2 Summary of key findings

The novel methods employed to perform field evaluation of combustion-related air pollutants were established through literature (Jantunnen et al. 2002; Koehler and Peters, 2015) to provide strategies for exposure assessment in different environmental settings. Furthermore, the central problems addressed in this thesis are the identification of key pollutants from combustion-related sources and the imperative needs to quantify personal exposure using dedicated and reliable measurement techniques. The main key findings from this study divided into the development of novel methods and extended to evaluate combustion-related air pollutants atin indoor and outdoor settings are shown below.

8.2.1 The state-of-art methods of sampling and analysis of combustion-related air pollutants

  • In chapter 3, the development of methods is described for combustion-related air pollutants including PM, BC, NO₂ and pPAHs. The flexible and relevant techniques were developed to collect and analyse the air pollutant samples from simple, quick and low-cost to complex and prolonged systems. The performance of personal air sampling pumps and the real-time sensors primarily used during the course of this study were evaluated in the pilot experiments. The application of lower flow rate using Apex personal air sampling pumps couldan provide a stable flow calibration and were suitable for stationary and peripatetic sampling techniques to collect PM specimens.
  • In chapter 4, the field evaluation of collocated portable low power equipment against reference analyser demonstrates the calibration of the monitor to apply in the real world monitoring of combustion-related air pollutants.
  • The use of simple methods for non-destructive and low-cost optical analysis of sequentially loaded filter air samples described in Chapter 4 & 6 has demonstrated how BC can be estimated from filter reflectance and scanned filter image calibrated against co-located MicroAeth observations.
  • In chapter 5 & 6, the filter-based measurements of gravimetric and reflectometer were suggested to be a reliable technique to estimate PM mass and darkness of carbonaceous particles (BC) atin the indoor and outdoor settings.
  • In chapter 5, the use of additional real-time instruments to measure PM metrics (PM₁, PM₂.₅ and PM₁₀), NO₂, O₃ and CO₂ were demonstrated using Osiris, MicroPEM, LEO and CP 11. Both MicroAeth and MicroPEM provide sufficient accurate measurements at 5-minutes time intervals to measure BC and PM₂.₅ atin the indoor environment. Furthermore, the CP11 instrument proved to be practical for CO₂ measurements in the indoor area.
  • The application of portable real-time novel sensors described in Chapter 5, 6 & 7 had shown the use of MicroAeth is relevant to measure BC concentrations atin the indoor and outdoor settings. In contrast, the applicability of Aeroqual sensor for recording NO₂ levels is relevant to outdoor environment. Thus, the uses of passive samplers are more reliable when sampling in the indoor setting.

8.2.2 Evaluation of PM, BC and NO₂ exposure in the indoor and outdoor settings

  • The indoor field tests were carried out in the refurbished and existing office buildings during summer 2014 & 2016 at University of Strathclyde. Both of PM, BC and NO₂ indoor measurements were found influenced by the outdoor sources entered through natural ventilation and the location of buildings near the urban roadsides. The use of office equipment such as the printer for copying and printing activities is suggested to be one of the drivers for higher PM and BC concentrations in the office area. The CO₂ levels were found higher (>1000 ppm) when the ventilation system did not function properly.
  • The methods employed using filter-based sampling,sampling; passive samplers and real-time monitors were extended in the urban outdoor environment. The application of novel mobile and static platforms and wearable sensors were used to assess PM, BC and NO₂ while walking on a pre-defined route in Glasgow city centre during summer 2014 & 2015 and winter 2015. Measurements at two heights were simulated to investigate whether the combustion-related air pollutant concentrations at child pushchair and adult inhalation heights were different from one another at roadside locations. Meanwhile, another set of BC and NO₂ measurements were made using wearable and portable real-time sensors of MicroAeth and Aeroqual over different walking zone along a gradient of urban outdoor pollutions. Consistently increased PM₂.₅ mass concentrations (13.6 % increaseincreases in mean) and reflectance (19.2 % increase in mean) were observed at lower height (0.8 m) compared to upper height (1.68 m). The NO₂ concentrations may have a greater tendency to be higher at the ground.
  • Research also pointed out that the variation of BC and NO₂ measured in Glasgow central were mainly determined by street topography and rush hour period. Both BC and NO₂ concentrations measured at the near roadside were higher than the background measurements recorded by the AUN sites. The maximum values of BC and NO₂ were recorded along the street canyon walking area at Hope St. (24.5 for BC and 138.3 µg m¯³ for NO₂). The average BC and NO₂ concentrations during mid-day observations were found 22% higher compared to morning and afternoon measurements along campus site walking routes.
  • Mobile measurements at varying distances from sources of diesel exhaust emissions were carried out in Poland as part of the study case described in Chapter 7. The result displays shows marked elevations of BC and NO₂ concentrations and were observed in downwind proximity to industrial fracking equipment sources, where the average was 4 & 2 times higher respectively than measured during walking at the urban Glasgow city centre. However, there is no great difference between maximum NO₂ concentrations recorded at the hydraulic fracking test site (292.3 µg m¯³) and NO₂ levels measured in the urban Glasgow city centre (280.6 µg m¯³).

8.3 Summary of thesis contributions

This research presented a novel approach, which anticipate to provideproviding insights in personal exposure to combustion related air pollutant, therefore wouldwill opens the doors for exploring advanced methodologies between researchers, participants and other stakeholders. The main contributions of this study are:

(a) Provide alternate personal exposure assessment strategies to combustion-related air pollutants

The basis of the novel development approach in this study is the flexibility and effectiveness of sample collection and analysis systems for combustion-related air pollutants. By integrating novel exposure assessment along with measures of combustion related air pollutants concentrations and the use of portable real-time sensors and GPS receiver has allowed to approximate the exposure data and identify the spatial and temporal variability in the urban environment. Furthermore, the study at two vertical heights using moving and stationary platforms has been demonstrated to be superior, in terms of reliability and robustness to state-of-arts air monitoring alternatives in estimating the pollutant exposure to adult and children.

(b) Provide cost-effective technique

In chapter 3, a simple and low-cost method to estimate BC concentrations has introduced using reflectometer and an office scanner. From the results reported in Chapter 4 & 6, these approaches can be used to approximate BC values estimate exposures to combustion-related air pollutants in studies of the effects of air pollution on human health.

(c) Characterisation of combustion-related sources

The short time resolution of the types of portable instruments used in this study can help to identify the occupational (office worker and fracking site operator) and environmental exposure to combustion-related air pollutants. This research also characterise the combustion related air pollutant concentrations to the vulnerable group, the children who are prone to exposure ofe to the ambient air pollution in the urban environment.

(d) Useful starting point for occupational and environmental exposure near the industrial fracking site

Most of the population-base studies evaluating health effects from UNG development (McKenzie et al. 2012; McKenzie et al. 2014; Rabinowitz et al. 2015) have highlighted the need to provide exposure monitoring close proximity to the sources. The results presented in Chapter 7, suggest a promising field evaluation technique to assess combustion-related air pollutants of BC and NO₂ using dedicated high time resolutions of portable monitors in the real world environment during the operation of fracking diesel machinery. Although the measurement was undertaken in a short period due to limited access to the facility, this preliminary observation is beneficial for extended health risk assessment before, during, or after the UNG activities.

(e) Social, policy and guidelines impacts

The indoor study in chapter 5 has addressed the variables and sources of PM, BC and NO₂ with additional measurements of CO₂. This information may reflect the policy implication for the office building particularly in the existing building at Graham Hills Building, University of Strathclyde has to improve comfort and well-being of their office staff. Additionally, the urban outdoor study conducted in Glasgow city centre may characterise patterns of personal exposure during walking in the city centre districts. This will allow individual to make choice in order toto reduce their exposure to combustion-related air pollutants from the choice of their walking route. As mentioned in section 2.5, to date, there is no regulation for BC,BC; therefore the findings in this study will be beneficial for regulatory standard and threshold levels of BC related to its potential health effects.

8.4 Study limitation

This study suffers certainfrom some limitations, which have to be pointed out. They are as follows:

  • Interesting result that seemed to indicate the B[a]P] P concentrations from pPAHs profiles detected from GC-MS system, however, the study did not overextend to assess this pollutant atin the indoor and outdoor settings. This is because this study only considered PM, BC and NO₂ as the prime metrics for combustion-related air pollutants extended in both field tests, thus beyond the scope of this thesis.
  • The commercially advanced real-time monitors used in this study also have their drawbacks when deployed atin the indoor and outdoor environment. The gas sensor, Aeroqual wereas not sufficiently able to measure very low NO₂ concentrations with high resolutions particularly atin the indoor measurements. The air sensing devices wereare not waterproof, whereas the sampling exercises in the outdoor environment were weather dependable. This has constraint in the number of studies.
  • The use of single filter in order toto approximate measure BC concentrations from sequential sampling exercises might haveay introduced saturation effects from the deposited particles on the filter surface. As mentioned in section 4.3, the BC loading collected from the sampling system in this study were considered lower compared to other studies. This has resulted in the narrow measurement range, which wouldill effectaffect the performance of the proposed methods.
  • The extended measurements for indoor and urban outdoor settings were conducted only in the summer and winter,winter; the results need to be validated in the other seasons as well. Both of measurements were conducted in a separate sampling sessions using different monitoring techniques, therefore the results cannot be compared.
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8.5 Recommendation for future work

  • More studies are certainly requiredneeded for future research on determining the low concentrations of airborne particles to characterise and evaluate the pPAHs particularly the B[a]P concentrations. This perhaps will determine whether this pollutant component can be one of the proxy for the combustion-related air pollutant sources and beneficial for the health risk assessment in individual and population base.
  • Performance evaluation of wearable real-time sensors against the traditional way of air monitoring and reference methods to the various micro-environments would allow the data reliability and accuracy for exposure and health assessment. Therefore, simultaneous measurements with GPS data in different exposure scenarios wouldill be fully characterise in the short and long-term effects of combustion related air pollutants.
  • The range of BC loading could be expanded in the real world settings to ascertain the degree of this measurement which can approximate in a comprehensive scale. Additionally, to determine uncertainty from the newly developed BC measurement systems using calibrated sequential filter reflectance and scanned values, further test agreement with other calibrated method including thermal-optical analysis (Ramanathan et al. 2011) is required to increase the accuracy of the obtain estimates BC concentrations.
  • To investigate the relationship between indoor and outdoor particularly in the urban area, it is recommended that more studies are warrants with documented adverse health outcomes, air exchange rate of window opening behaviour during summer season and frequency of using printer in the office room. By combining time activity patterns and field evaluation of spatial-temporal, air pollutant concentrations could be expanded for exposure assessment, particularly to be of benefit to people exposed to high levels of combustion-related air pollution, including professional drivers, vehicle maintenance personnel and traffic wardens. Other determinants such as traffic density, traffic counts and seasonal factors must be taken into account in the future study. The use of wearable heart rate variability and blood pressure devices may allow for the health status data coupled with identification of peak exposures atin the indoor and outdoor settings where the concentration pollutants are varied in time and space. This also will also allow the advance knowledge of acute and chronic exposures into better understanding of the environmental and occupational studies where the innovative science and creative engineering are the essentials.

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