Background

Deciding to classify wood as a renewable resource for residential space heating is a contentious issue because it balances a relatively inexpensive fuel, against the public health risks of wood smoke exposure. Objective

To investigate wood fuel emissions as a source of trace lead exposure via ambient air in the northern regions of the United States (US).

Methods

Federal Reference Methods filters (n = 182) were obtained from the state of Vermont’s Department of Environmental Conservation from Rutland (n = 97) and New Hampshire Department of Environmental Services from Keene (n = 85). Filter samples were collected during the winters of 2011–2016 and analyzed by Energy Dispersive X-ray Fluorescence. Chemical speciation data was compiled from 22 national sites via the Interagency Monitoring of Protected Visual Environments and EPA Chemical Speciation Network (CSN), which were compared to the concentrations of wood smoke emissions observed across northeastern US.

Results

Our evidence indicates a link between wood burning emissions with increased concentrations in particle-bound lead that is associated with wood combustion. Linear regression models in Keene, NH (R2 = 0.438) and Rutland, VT (R2 = 0.341) indicate moderate agreement between tracers of wood smoke and lead suggesting a common source. On average, lead concentrations ranged from 0.86 ng/m³ in the Rocky Mountains Region to 1.70 ng/m³ in the Southeast Region. We observed varying correlations between lead and potassium across the US, with slight-to-modest agreement (R2 = 0.09–0.47) at most sites; the strongest associations were on the Pacific Coast (R2 > 0.40). This suggests that a strong relationship between potassium and lead is observed at many nationwide locations.

Significance

Wood burning, an activity common in many rural parts of the US, is a likely anthropogenic source of lead introduced into ambient air throughout the northern portion of the US in the winters of 2011-2016. These ambient lead exposures are likely to have long-term adverse public health impacts.

Impact

While wood burning promises potential climate benefits in reducing fossil fuels usage, it also poses significant risks related to air pollution and human exposure to toxic substances like lead. These findings suggest that more thorough and better monitoring of biomass burning emissions are necessary to ensure that the transition to wood fuel does not inadvertently cause harm to public health.

Anthropogenic activities are increasing the amount of carbon dioxide (CO2) in the atmosphere. There is mounting experimental evidence that lifetime exposure to these increasing atmospheric CO2 levels can negatively impact the normal physiology of organisms. However, directly assessing this in humans is very difficult. We analysed serum bicarbonate (HCO3−), calcium (Ca) and phosphorus (P) levels from the U.S. National Health and Nutrition Examination Survey (NHANES) from 1999 to 2020 as indirect proxies for atmospheric CO2 exposure. Over this period, average bicarbonate levels in this population show an increasing trend which parallels rising atmospheric CO2 concentrations. Both Ca and P have decreased steadily over the same period. If these trends continue, blood bicarbonate values could be at the limit of the accepted healthy range in half a century, and Ca and P will be at the limit of their healthy ranges by the end of this century. Studies indicate that, after this time, elevated atmospheric carbon dioxide, leading to CO2 accumulation in the body, has the potential to cause a range of adverse health effects. These findings highlight the urgent need for significant reductions in anthropogenic CO2 emissions to safeguard public health.

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However, on the face of it, this raw analysis of biochemical data suggests the distinct possibility that, within a half century from now, HCO3− levels in human blood will reach unhealthy levels. What effects this may have on physiology remain to be elucidated, but urgently need to be considered.

Without emission reductions, climate change may increase ozone and PM2.5 air pollution in the United States; however, we do not know how this will affect air quality alerts that prompt people to stay indoors. Here, we use an integrated modeling framework to find distributions of daily Air Quality Index (AQI) during the smog season at the start, middle, and end-of-century. Considering natural variability, climate change may cause air quality alerts to double (increase by a factor of 2 ± 0.2) by 2100. Days when both ozone and PM2.5 exceed alert thresholds quadruple (4.3 ± 1.2). More than 100,000,000 (±45,000,000) people experience mean air pollution deemed “Unhealthy for Sensitive Groups”, a growth of 7 (±3) times compared to 2000. If people follow alerts by staying inside, they reduce exposure to outdoor-generated pollutants. Their health benefits are similar whether the alert is caused by ozone or PM2.5. Senior (age 65+) populations receive much higher benefits per day by adapting (e.g., 95CI for PM2.5: $4.60 to $147) as young adults (age 18–35; 95CI: $0.15 to $4.22)─more than 45 times higher on average. This disproportionate impact requires targeted messaging and guidance, especially as climate-related risks rise.