People who are consistently exposed to both wood smoke and tobacco smoke are at a greater risk for developing chronic obstructive pulmonary disease (COPD慢性阻塞性肺炎) and for experiencing more frequent and severe symptoms of the disease, as well as more severe airflow obstruction, than those who are exposed to only one type of smoke, according to the results of a new population-based study conducted by researchers in Colombia. The results of the study will be presented at the ATS 2013 International Conference.

Concerns continue to grow about the effects of climate change on fire. Wildfires are expected to increase 50 percent across the United States under a changing climate, over 100 percent in areas of the West by 2050 as projected by some studies. Of equal concern to scientists and policymakers alike are the atmospheric effects of wildfire emissions on climate. A new article published in the journal Forest Ecology and Management by U.S. Forest Service scientists synthesizes recent findings on the interactions between fire and climate and outlines future research needs. Authored by research meteorologists Yongqiang Liu and Scott Goodrick from the Forest Service Southern Research Station (SRS) and Warren Heilman from the Northern Research Station, the article homes in on the effect of emissions from wildfires on long-term atmospheric conditions.

"While research has historically focused on fire-weather interactions, there is increasing attention paid to fire-climate interactions," says Liu, lead author and team leader with the SRS Center for Forest Disturbance Science. "Weather, the day-to-day state of the atmosphere in a region, influences individual fires within a fire season. In contrast, when we talk about fire climate, we're looking at the statistics of weather over a certain period. Fire climate sets atmospheric conditions for fire activity in longer time frames and larger geographic scales."

Wildfires impact atmospheric conditions through emissions of gases, particles, water, and heat. Some of the article focuses on radiative forcing from fire emissions. Radiative forcing refers to the change in net (down minus up) irradiance (solar plus longwave) at the tropopause, the top of the troposphere where most weather takes place.

Smoke particles can generate radiative forcing mainly through scattering and absorbing solar radiation (direct radiative forcing), and modifying the cloud droplet concentrations and lifetime, and hence the cloud radiative properties (indirect radiative forcing). The change in radiation can cause further changes in global temperatures and precipitation.

"Wildfire emissions can have remarkable impacts on radiative forcing," says Liu.

"During fire events or burning seasons, smoke particles reduce overall solar radiation absorbed by the atmosphere at local and regional levels. At the global scale, fire emissions of carbon dioxide contribute substantially to the global greenhouse effect."

Other major findings covered in the synthesis include: The radiative forcing of smoke particles can generate significant regional climate effects, leading to lower temperatures at the ground surface. Smoke particles mostly suppress cloud formation and precipitation. Fire events could lead to more droughts. Black carbon, essentially the fine particles of carbon that color smoke, plays different roles in affecting climate. In the middle and lower atmosphere, its presence could lead to a more stable atmosphere. Black carbon plays a special role in the snow-climate feedback loop, accelerating snow melting. 

Land surface changes may be triggered that also play into future effects. "Wildfire is a disturbance of ecosystems," says Liu. "Besides the atmospheric impacts, wildfires also modify terrestrial ecosystem services such as carbon sequestration, soil fertility, grazing value, biodiversity, and tourism. The effects can in turn trigger land use changes that in turn affect the atmosphere."

The article concludes by outlining issues that lead to uncertainties in understanding fire-climate interactions and the future research needed to address them.

"Although previous studies have shown a definite link between wood smoke exposure and the development of COPD, those studies were case-controls and case series of patients with similar disease or health profiles," said study lead author Carlos Torres-Duque, M.D., director of research at the Fundacion Neumologica Colombiana in Bogota. "This new data derives from a population-based study that looked at wood smoke exposure and the overall prevalence of COPD, as well as the characteristics of the disease and those who suffer from it."

About 40 percent of the world's population uses solid fuels -- especially wood -- for cooking or heating, he noted.

For this study, Dr. Torres-Duque and his colleagues used data from the PREPOCOL (Prevalencia de la Enfermedad Pulmonar Obstructiva Crónica en Colombia) study which evaluated the prevalence of COPD among the adult residents of five Colombian cities. The study included 5,539 subjects, 8.9 percent of whom were diagnosed with COPD. The study participants were divided into four groups: those who were exposed to wood smoke and who had never smoked tobacco (30.9 percent); those who were exposed to tobacco smoke but had no exposure to wood smoke (18.7 percent); those who had been exposed to both types of smoke (29.8 percent); and those who had exposure to neither type of smoke (20.6 percent).

Patients' lung function was measured using spirometry（呼吸量测定法）, a technique used to measure the amount of air a person is able to inhale and exhale, and all patients completed a standardized respiratory questionnaire to identify exposure to smoke.

In their initial review of data, the researchers learned that 53 percent of those diagnosed with COPD had both wood and tobacco smoke exposure; moreover, the prevalence of COPD increased as exposure to wood smoke increased.

After adjusting for specific factors including age, active and passive tobacco smoking, education level, history of TB and altitude, the researchers found that wood smoke exposure of 10 or more years posed a significant risk factor for developing COPD in both men and women and those with both wood and tobacco exposure had poorer lung function scores and more phlegm（痰，粘液） and coughed more frequently than those who had exposure to only one type of smoke. Among the COPD population, those who were exposed only to wood smoke tended to be women, to have higher BMIs and to be shorter than those exposed to tobacco smoke or to a combination of wood and tobacco smoke.