标题：Effectiveness of Residential Wood-Burning Regulation on Decreasing Particulate Matter Levels and Hospitalizations in the San Joaquin Valley Air Basin
摘要：Objectives. We examined the impact of Rule 4901, aimed at reducing residential wood burning, on particulate matter levels and hospitalizations in the San Joaquin Valley Air Basin (SJVAB). Methods. Using general linear mixed models and generalized estimating equation models, we compared levels of particulate matter and of hospital admissions (age groups = 45–64 and ≥ 65 years) in the SJVAB for cardiovascular disease (CVD), ischemic heart disease (IHD), and chronic obstructive pulmonary disease during the burn seasons before (2000–2003) and after (2003–2006) implementation. Results. After implementation, we observed reductions of 12%, 11%, and 15% in particulate matter 2.5 micrometers in diameter or smaller (PM2.5), and 8%, 7%, and 11% in coarse particles, in the entire SJVAB and in rural and urban regions of the air basin, respectively. Among those aged 65 years and older, Rule 4901 was estimated to prevent 7%, 8%, and 5% of CVD cases, and 16%, 17%, and 13% of IHD cases, in the entire SJVAB and in rural and urban regions, respectively. Conclusions. The study suggests that Rule 4901 is effective at reducing wintertime ambient PM2.5 levels and decreasing hospital admissions for heart disease among people aged 65 years and older. The San Joaquin Valley Air Basin (SJVAB) extends from the Sacramento–San Joaquin Delta in the north to the Tehachapi Mountains in the south and from coastal mountain ranges in the west to the Sierra Nevada in the east. The SJVAB is an agricultural valley and includes the counties of Fresno, Kern, Kings, Madera, Merced, San Joaquin, Stanislaus, and Tulare. The San Joaquin Valley has hot dry summers and cold rainy winters characterized by dense low fog. Surrounded by mountains and lacking prevailing winds to disperse pollutants, the valley has historically had some of the worst air quality in California. 1,2 From 2001 to 2003, the ambient levels of PM2.5 (particulate matter ≤ 2.5 µm in diameter) in the SJVAB reached concentrations that were substantially greater than the 24-hour national standard at that time (65 µg/m3). 3 Combustion of solid fuels, such as wood, has been identified as the largest individual source of particulate matter during winter months, and has been estimated to generate as much as 23 tons per day of particles from smoke, soot, and ash. 4 The most severe particulate air pollution episodes in the SJVAB historically have occurred during winter months (November–February), during which residential fuel combustion has been estimated to contribute more than 20 metric tons per day of PM2.5 pollution to the SJVAB. 5 Because of this poor air quality, and to help attain the National Ambient Air Quality Standards and improve health, the San Joaquin Valley Unified Air Pollution Control District in 1992 adopted Rule 4901, which aimed at reducing emissions of carbon monoxide and particulates from residential wood-burning fireplaces and heaters 6 during the burn season (November–February) and establishing a public health education program to reduce wood-burning emissions. The rule was amended in 2003 to require mandatory curtailment of residential wood burning when air quality was forecast to be poor—that is, an air quality index of at least 150 (approximately 65 µg/m3 of PM2.5)—and other measures were taken to reduce the impact of residential burning. 7 Using the US Environmental Protection Agency’s software program BenMAP, Lighthall et al. estimated that the potential health benefits of the rule would be substantial, including reductions in several morbidity endpoints. 8 Epidemiological studies have found that exposure to the constituents of residential wood smoke is associated with reduced lung function, increased respiratory symptoms, and exacerbation of respiratory diseases, including chronic obstructive pulmonary disease (COPD) and asthma as well as respiratory-related emergency department and hospital visits. 9–23 Some studies have also shown that wood smoke is associated with adverse cardiovascular health effects. 13,14,24–27 In addition, controlled studies of wood smoke exposure found increases in markers of inflammation and coagulation, irritated mucosa, and increases in central arterial stiffness as well as a reduction in heart rate variability. 26,28–30 Concern over air quality has prompted several communities in the SJVAB to work with the district to regulate and ban residential burning when air quality forecasts are poor. These regulations have been coupled with public education, and there are indications that some of these campaigns have been successful in improving air quality. 4 The 2012 PM2.5 plan for the San Joaquin Valley includes a descriptive analysis of Rule 4901’s effectiveness in reducing PM2.5 concentrations in the Fresno area. 31 Since the regulation was fully implemented in 2003, however, no multivariate analysis has been performed to evaluate the changes in PM2.5 levels and health in response to district actions to regulate residential wood burning. We therefore evaluated the effectiveness of Rule 4901 in decreasing wintertime particulate matter such as PM2.5 and coarse particles in the SJVAB and in reducing the burden of wintertime hospital admission rates for cardiovascular disease (CVD), ischemic heart disease (IHD), and COPD in adults aged 45 to 64 years and in the elderly (≥ 65 years) residing in the SJVAB. Because the prevalence of wood burning as a heating fuel may vary by region, we also performed stratified analyses on the rural and urban regions of the SJVAB to address the nonuniformity of wood burning as a heating fuel among different regions of the valley. Although the rule was adopted in 1992, enforcement of the rule did not begin until the 2003 amendment. Therefore, for this study, we evaluated the impact of the rule on health and exposure during the burn season (November–February) for the 3 years before and after the 2003 amendment.
