How and Why AMC Collects Clouds on Mount Washington

cloud catching mount washington
PAULA CHAMPAGNEAMC’s cloud-catcher sits just a few hundred feet from the Lakes of the Clouds Hut and just below the summit of Mount Washington.


Just below Mount Washington’s summit, a cozy hut sits tucked in a cloud. A warm glow emanates from its rustic windows, as the scent of fresh bread and hums of conversation are swept up in the breeze. Someone dashes outside. Scampering over the rocks and past the lake with two sample bottles in hand, this shadowy figure makes its way to the weather station. Rain falls, a brisk wind blows along the ridge and a funny-looking box on a tripod wiggles in the wind. This is the cloud catcher, and it is hard at work.

Every summer since 1984, AMC’s Lakes of the Clouds Hut has housed a croo member tasked with the collection of cloud and rain samples. These samples will become part of a larger data set that has been gathered over 37 years. That work, those soggy days, translate into an understanding and scorecard for immensely successful past policy directives such as the Clean Air Act. What’s more, this data set provides accountability for humanity’s actions and impacts on the environment.

To sample the contents held within the clouds that envelop Mount Washington, a special cloud-catching box is used. For the cloud-catcher to work, the cloud, composed of tiny water droplets, must be blown through baffles—plastic guards that keep the rain out but allow a set of Teflon strands to precipitate out the liquid in the cloud into a collection bottle for a cloud-only sample.

The samples are analyzed for sulfate, nitrate, ammonium, and hydrogen ions. The burning of fossil fuels such as coal, gas, and oil emits these pollutants into the atmosphere. These pollutants can be human health hazards as well as dangerous to ecosystems. In the air, the sulfur dioxides and nitrogen oxides react with water and oxygen to form sulfuric and nitric acids.

Cloud cover in areas with high amounts of air pollution can be particularly harmful to red spruce, balsam fir, and fish species downstream, as clouds can be up to 20 times more acidic than rain. Mount Washington’s summit is in the clouds 51 percent of the time, and the thin soil cover makes the alpine environment particularly susceptible to damage from acidic pollutants.

In the 1980s, nearly 80 percent of the red spruce trees here had signs of “winter burning,” a secondary impact from the high acidity of the clouds and rain due to pollution in the air. The acid leached out protective compounds that protect spruce needles from damage by frigid temperatures. Those acidic pollutants migrated through the ecosystem, damaging ecosystem health across the White Mountain National Forest. Luckily, these very visible changes to this and other ecosystems were observed, and policy was enacted.

COURTESY OF SOPHIA GILLIESLakes of the Clouds Research Intern Sophia Gillies.

In 1990, Clean Air Act Amendments targeting acid rain were implemented. Long-term data sets from monitoring and observations of the climate were critical to creating the political pressure backing these policies. The data showed us the reality of the problem and continues to hold us accountable for our impact. The amendments, based on science, targeted and reduced air pollution that was making our air unsafe to breathe and hurting our ecosystems.

AMC’s data from the long-term monitoring of the cloud and rain acidity on Mount Washington mirror the legislative success of the Clean Air Act. Each year we continue to see a decline in sulfate and nitrate concentrations in the clouds we collect and other researchers have seen red spruce recovery.  We will continue the monitoring to learn and report how the cloud and rain chemistry impacts downstream ecosystems. Our air quality monitoring may also allow us to track events such as major forest fires across the country—which have become more common as a result of drought and climate change. This will contribute to our further understanding of the impact and distribution of those pollutants.

It is important that we don’t just celebrate our cleaner clouds and air, but rather that we take them as a lesson for our future.

The United Nations’ Intergovernmental Panel on Climate Change recently met and released the 2021 Climate Report. This report, based on science and created with data collection and observation, once again states the reality of our current climate crisis and the dire need for change to protect the planet we live on. We are at a critical moment in human history, and the success of the Clean Air Act highlights our ability to create lasting change. It is time we do that again.

About the Author…

Sophia Gillies

Sophia was AMC's Lakes of the Clouds Research Intern in 2021.

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