ENVIRONMENTAL EXPOSURE

Indoor nitrous acid and respiratory symptoms and lung function in adults

D L Jarvis¹, B P Leaderer², S Chinn¹, P G Burney¹

¹ Division of Population Sciences and Health Care Research, King’s College, London SE1 3QD, UK
² Centre for Perinatal Paediatric and Environmental Epidemiology, Department of Epidemiology and Public Health, Yale University School of Medicine, New Haven, Connecticut, USA

Correspondence to:
Correspondence to:
Dr D Jarvis
Division of Population Sciences and Health Care Research, King’s College, 42 Weston Street, London SE1 3QD, UK; deborah.jarvis{at}kcl.ac.uk

Background: Nitrogen dioxide (NO₂) is an important pollutant of indoor and outdoor air, but epidemiological studies show inconsistent health effects. These inconsistencies may be due to failure to account for the health effects of nitrous acid (HONO) which is generated directly from gas combustion and indirectly from NO₂.

Methods: Two hundred and seventy six adults provided information on respiratory symptoms and lung function and had home levels of NO₂ and HONO measured as well as outdoor levels of NO₂. The association of indoor HONO levels with symptoms and lung function was examined.

Results: The median indoor HONO level was 3.10 ppb (IQR 2.05–5.09), with higher levels in homes with gas hobs, gas ovens, and in those measured during the winter months. Non-significant increases in respiratory symptoms were observed in those living in homes with higher HONO levels. An increase of 1 ppb in indoor HONO was associated with a decrease in forced expiratory volume in 1 second (FEV₁) percentage predicted (–0.96%; 95% CI –0.09 to –1.82) and a decrease in percentage FEV₁/forced vital capacity (FVC) (–0.45%; 95% CI –0.06 to –0.83) after adjustment for relevant confounders. Measures of indoor NO₂ were correlated with HONO (r = 0.77), but no significant association of indoor NO₂ with symptoms or lung function was observed. After adjustment for NO₂ measures, the association of HONO with low lung function persisted.

Conclusion: Indoor HONO levels are associated with decrements in lung function and possibly with more respiratory symptoms. Inconsistencies between studies examining health effects of NO₂ and use of gas appliances may be related to failure to account for this association.

Abbreviations: FEV₁, forced expiratory volume in 1 second; FVC, forced vital capacity; HONO, nitrous acid; NO₂, nitrogen dioxide; SOB, shortness of breath

Keywords: nitrogen dioxide; nitrous acid; asthma

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