Measurement and analysis of personal exposure to nitrogen dioxide from indoor and outdoor sources

The study of exposure to nitrogen dioxide (NO2) is important because of its significant health effects. As it is associated with combustion processes, road traffic is one of the main outdoor sources and gas cookers and gas heaters are the main indoor sources. Indoor NO2 is a significant health problem due to people spending most of their time indoors. Activity patterns and lifestyles vary and, consequently, people may be exposed NO2 from several different sources during a typical day. In order to understand and quantify total personal exposure, it is, therefore, important to determine both the indoor and outdoor concentration levels. This thesis reports on two pilot studies, spring and summer 2000 and three full campaigns, autumn, winter 2000 and summer 2001 to investigate the relationship between NO2 personal exposure of office workers in relation to indoor and outdoor sources and activity patterns. The study has been carried out in the area of Hertfordshire, UK. This region is adjacent to London and has a population of just over one million people. It consists of several major commuter routes connecting medium sized towns to London. Volunteers using gas cookers and electric cookers in their kitchens were asked to fill in activity patterns records and questionnaires. At the same time, weekly average personal exposure to N02 and indoor (bedroom, living room, kitchen and office) and front door N02 concentrations were measured by using passive diffusion tubes. Correlation between weekly personal exposures and mean indoor and outdoor concentrations during the same periods were examined. The results show significant differences in indoor and outdoor concentrations of NO2 in autumn and winter. The data indicated that NO2 concentrations in all rooms in houses with gas cookers were significantly higher than those with electric cookers especially in kitchens where levels of NO2 were 3 to 4 times greater. Interpretation of time activity daily diaries showed that the subjects spent on average 80% of their time indoors. Despite the very high concentrations in kitchens with gas cookers, personal exposure did not increase similarly as volunteers only spent a small amount of time cooking over the 7 day period. Good correlation was observed between the average indoor NO2 concentrations, especially in bedrooms and living rooms, and personal exposure. This indicated that indoor levels in areas like the bedroom and living rooms could be used as a proxy for NO2 personal exposure for this group of volunteers. An empirical time weighted average concentration model was developed based on the NO2 concentrations measured in the microenvironments and the data on time spent in each microenvironment. This was tested by comparison between time weighted average calculations and the personal exposure measurements of NO2 concentrations. The comparison yielded good relationships for most of the campaign periods despite the fact that NO2 concentrations were not similar in the different micro environments and the fact that subjects spent varying times in these places. Statistical tests were performed for time weighted average concentrations of N02 and the personal exposure to NO2 concentrations and differences were found to be non-significant

Activity pattern and personal exposure to nitrogen dioxide in indoor and outdoor microenvironments

People are exposed to air pollution from a range of indoor and outdoor sources. Concentrations of nitrogen dioxide (NO2), which is hazardous to health, can be significant in both types of environments. This paper reports on the measurement and analysis of indoor and outdoor NO2 concentrations and their comparison with measured personal exposure in various microenvironments during winter and summer seasons. Furthermore, the relationship between NO2 personal exposure in various microenvironments and including activities patterns were also studied. Personal, indoor microenvironments and outdoor measurements of NO2 levels were conducted using Palmes tubes for 60 subjects. The results showed significant differences in indoor and outdoor NO2 concentrations in winter but not for summer. In winter, indoor NO2 concentrations were found to be strongly correlated with personal exposure levels. NO2 concentration in houses using a gas cooker was higher in all rooms than those with an electric cooker during the winter campaign, whereas there was no significant difference noticed in summer. The average NO2 levels in kitchens with a gas cooker were twice as high as those with an electric cooker, with no significant difference in the summer period. A time-weighted average personal exposure was calculated and compared with measured personal exposures in various indoor microenvironments (e.g. front doors, bedroom, living room and kitchen); including non-smokers, passive smokers and smoker. The estimated results were closely correlated, but showed some underestimation of the measured personal exposures to NO2 concentrations. Interestingly, for our particular study higher NO2 personal exposure levels were found during summer (14.0 ± 1.5) than winter (9.5 ± 2.4).Peer reviewe

Impact of COVID-19 lockdown on NO2 and PM2.5 exposure inequalities in London, UK

Amid the COVID-19 pandemic, a nationwide lockdown was imposed in the United Kingdom (UK) on 23rd March 2020. These sudden control measures led to radical changes in human activities in the Greater London Area (GLA). During this lockdown, transportation use was significantly reduced and non-key workers were required to work from home. This study aims to understand how population exposure to PM2.5 and NO2 changed spatially and temporally across London, in different microenvironments, following the lockdown period relative to the previous three-year average in the same calendar period. Our research shows that population exposure to NO2 declined significantly (52.3% ±6.1%), while population exposure to PM2.5 showed a smaller relative reduction (15.7% ±4.1%). Changes in population activity had the strongest relative influence on exposure levels during morning rush hours, when prior to the lockdown a large percentage of people would normally commute or be at the workplace. In particular, a very high exposure decrease was observed for both pollutants (approximately 66% for NO¬2 and 19% for PM2.5) at 08:00am, consistent with the radical changes in population commuting. The infiltration of outdoor air pollution into housing modifies the degree of exposure change both temporally and spatially. Moreover, this study shows that the impacts on air pollution exposure vary across groups with different socioeconomic status (SES), with a disproportionate positive effect on the areas of the city home to more economically deprived communities

Measured and modeled personal and environmental NO2 exposure

Background: Measured or modeled levels of outdoor air pollution are being used as proxies for individual exposurein a growing number of epidemiological studies. We studied the accuracy of such approaches, in comparison withmeasured individual levels, and also combined modeled levels for each subject’s workplace with the levels at theirresidence to investigate the influence of living and working in different places on individual exposure levels. Methods: A GIS-based dispersion model and an emissions database were used to model concentrations of NO2atthe subject’s residence. Modeled levels were then compared with measured levels of NO2. Personal exposure wasalso modeled based on levels of NO2at the subject’s residence in combination with levels of NO2at theirworkplace during working hours. Results: There was a good agreement between measured façade levels and modeled residential NO2levels (rs = 0.8,p > 0.001); however, the agreement between measured and modeled outdoor levels and measured personalexposure was poor with overestimations at low levels and underestimation at high levels (rs = 0.5, p > 0.001 andrs = 0.4, p > 0.001) even when compensating for workplace location (rs = 0.4, p > 0.001). Conclusion: Modeling residential levels of NO2 proved to be a useful method of estimating façade concentrations.However, the agreement between outdoor levels (both modeled and measured) and personal exposure was,although significant, rather poor even when compensating for workplace location. These results indicate thatpersonal exposure cannot be fully approximated by outdoor levels and that differences in personal activity patternsor household characteristics should be carefully considered when conducting exposure studies. This is an importantfinding that may help to correct substantial bias in epidemiological studies