We estimated the size-resolved particle deposition rates for the ultrafine and submicrometer particles using a nonlinear regression method with unknown particle background concentrations during nonsourced period following a controlled sourced period in a well-mixed residential environment. A dynamic adjustment method in conjunction with the constant injection of tracer gas was used to maintain the air exchange rate at three target levels across the range of 0.61-1.24 air change per hour (ACH). Particle deposition was found to be highly size dependent with rates ranging from 0.68 ± 0.10 to 5.03 ± 0.20 h(-1) (mean ± s.e.). Our findings also suggest that the effect of air exchange on the particle deposition under enhanced air mixing was relatively small when compared to both the strong influence of size-dependent deposition mechanisms and the effects of mechanical air mixing by fans. Nonetheless, the significant association between air exchange and particle deposition rates for a few size categories indicated potential influence of air exchange on particle deposition. In the future, the proposed approach can be used to explore the separate or composite effects between air exchange and air mixing on particle deposition rates, which will contribute to improved assessment of human exposure to ultrafine and submicrometer particles.

We validated the use of the mass balance model to determine the effectiveness of portable air purifiers in removing ultrafine (<0.10 μm) and submicrometer particles (0.10-0.53 μm) in an apartment. We evaluated two identical portable air purifiers, equipped with high efficiency particulate air filters, for their performance under three different air flow settings and three target air exchange rates: 0.60, 0.90, and 1.20 h(-1). We subsequently used a mixed effects model to estimate the slope between the measured and modeled effectiveness by particle size. Our study showed that effectiveness was highly particle size-dependent. For example, at the lowest target air exchange rate, it ranged from 0.33 to 0.56, 0.51 to 0.75, and 0.60 to 0.81 for the three air purifier flow settings, respectively. Our findings suggested that filtration was the dominant removal mechanism for submicrometer particles, whereas deposition could play a more important role in ultrafine particle removal. We found reasonable agreement between measured and modeled effectiveness with size-resolved slopes ranging from 1.11 ± 0.06 to 1.25 ± 0.07 (mean ± SE), except for particles <35 nm. Our study design can be applied to investigate the performances of other portable air purifiers as well as the influences of various parameters on effectiveness in different residential settings.

As the frequency and intensity of wildfires are projected to globally amplify due to climate change, there is a growing need to quantify the impact of exposure to wildfires in vulnerable populations such as adolescents. In our study, we applied rigorous causal inference methods to estimate the effect of wildfire exposure on academic performance of high school students in Brazil between 2009 and 2015. Using longitudinal data from 8,183 high schools across 1,571 municipalities in Brazil, we estimated that the average performance in most academic subjects decreases under interventions that increase wildfire exposure, e.g., a decrease of 1.8% (p= 0.01) in the natural sciences when increasing the wildfire density from 0.0035 wildfires/km2(first quantile in the sample) to 0.0222 wildfires/km2(third quartile). Furthermore, these effects considerably worsened over time and were worse in regions with lower income. Our findings highlight the adverse impact of wildfires on educational outcomes.

Globalization has prompted cross-cultural migration in search of employment opportunities, and poor adaptation during acculturation is widely known to cause additional psychosocial stress. Hence, the objective of this study was to investigate migrant workers’ perceptions of acculturation, identify work-related stressors, and understand the respective coping strategies among male Indonesians in the manufacturing industry, particularly during the COVID-19 pandemic. Fifteen workers were recruited and interviewed on their acculturation experiences. We found that the workers were susceptible to forced adaptation to stressful conditions relating to work organization, economic distress, interaction with the manpower agencies, language barriers, and so on. During the pandemic, workers experienced overload, economic hardship, suspended home visits, isolation, discrimination, and fear of cluster infection in the crowded dormitory. We also found that workers were able to adopt coping strategies by capitalizing on resources at the individual, institutional, and governmental policy levels to actively solve problems, increase emotional support, and fortify self-appraisals. The identified coping strategies could inform policy development to assist with positive adaptation and promote the well-being of the migrant worker population.