Background

Kilauea Volcano on the Island of Hawai'i has erupted continuously since 1983, releasing approximately 300–12000 metric tons per day of sulfur dioxide (SO₂). SO₂ interacts with water vapor to produce an acidic haze known locally as “vog”. The combination of wind speed and direction, inversion layer height, and local terrain lead to heterogeneous and variable distribution of vog over the island, allowing study of respiratory effects associated with chronic vog exposure.

Objectives

We characterized the distribution and composition of vog over the Island of Hawai'i, and tested the hypotheses that chronic vog exposure (SO₂ and acid) is associated with increased asthma prevalence, respiratory symptoms, and reduced pulmonary function in Hawai'i Island schoolchildren.

Methods

We compiled data of volcanic emissions, wind speed, and wind direction over Hawai'i Island since 1992. Community-based researchers then measured 2- to 4-week integrated concentrations of SO₂ and fine particulate mass and acidity in 4 exposure zones, from 2002 to 2005, when volcanic SO₂ emissions averaged 1600 metric tons per day. Concurrently, community researchers recruited schoolchildren in the 4th and 5th grades of 25 schools in the 4 vog exposure zones, to assess determinants of lung health, respiratory symptoms, and asthma prevalence.

Results

Environmental data suggested 4 different vog exposure zones with SO₂, PM2.5, and particulate acid concentrations (mean ± s.d.) as follows: 1) Low (0.3 ± 0.2 ppb, 2.5 ± 1.2 μg/m³, 0.6 ± 1.1 nmol H +/m³), 2) Intermittent (1.6 ± 1.8 ppb, 2.8 ± 1.5 μg/m³, 4.0 ± 6.6 nmol H +/m³), 3) Frequent (10.1 ± 5.2 ppb, 4.8 ± 1.9 μg/m³, 4.3 ± 6.7 nmol H +/m³), and 4) Acid (1.2 ± 0.4 ppb, 7.2 ± 2.3 μg/m³, 25.3 ± 17.9 nmol H +/m³). Participants (1957) in the 4 zones differed in race, prematurity, maternal smoking during pregnancy, environmental tobacco smoke exposure, presence of mold in the home, and physician-diagnosed asthma. Multivariable analysis showed an association between Acid vog exposure and cough and strongly suggested an association with FEV1/FVC < 0.8, but not with diagnosis of asthma, or chronic persistent wheeze or bronchitis in the last 12 months. Conclusions: Hawai'i Island's volcanic air pollution can be very acidic, but contains few co-contaminants originating from anthropogenic sources of air pollution. Chronic exposure to acid vog is associated with increased cough and possibly with reduced FEV1/FVC, but not with asthma or bronchitis. Further study is needed to better understand how volcanic air pollution interacts with host and environmental factors to affect respiratory symptoms, lung function, and lung growth, and to determine acute effects of episodes of increased emissions.