Abstract
Background: The relationship between NO2 and asthma has been investigated; however, the WHO (2005) has reported that it is unclear to what extent the health effects observed in epidemiological studies are attributable to NO2 itself or to the other primary and secondary combustion-related products with which it is typically correlated.
Objectives: To obtain a reasonable hypothesis for the contradictions concerning relationships between NO2 and asthma symptoms by this descriptive epidemiological study.
Methods: We examined the relationships between indoor and monitoring station NO2, indoor HONO (primary combustion-related products, decomposed by sunlight, generated from NO2 after sunset), and self-reported asthma symptoms from 2010 through 2012 for five childhood asthma patients per year in Kishiwada, Japan, from autumn to winter. We used a simple Mann-Whitney U-test and r2 to examine relationships between the various data for the entire study period and for the first half of the study period.
Results: Monitoring station NO2 was significantly associated with self-reported mild asthma attacks in the first half of the study period in 2012, 2011-2012, and 2010-2012 according to U-tests, but not over the entire study period. Moreover, indoor NO2, which was usually higher in concentration than monitoring station NO2, was not significantly associated with self-reported mild asthma attacks in both study periods or any year. Indoor HONO was significantly associated with self-reported mild asthma attacks in the first half of the study period in 2010, 2010-2011, and 2011-2012. Indoor HONO was correlated with monitoring station NO2 in 2011 (r2 = 0.97) and 2012 (r2 = 0.55), as well as with indoor NO in 2010 (r2 = 0.75) in the first half of the study period.
Conclusion: We hypothesize that HONO is a more important nitrogen oxide in mild asthma attacks than NO2 and that the significant association between monitoring station NO2 and mild asthma attacks depends on HONO generated from outdoor NO2 at night.
