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If you’re of a certain age, you probably remember the hole in the ozone layer. Like Joseph Kony and Livestrong wristbands, the obsession over O3 now feels like a cultural artifact, thanks to ozone depletion being one of the rare success stories of international environmental cooperation. Since the world banned chlorofluorocarbons under the Montreal Protocol in 1987, the holes over the North and South poles have steadily recovered.
Today, if you hear about “ozone” at all, it’s much more likely to be from an air quality alert on your phone. Unlike the stratospheric ozone that we were all so concerned about in the 1980s and 1990s, which makes up a protective layer around the planet that insulates us from the sun’s cancer-causing ultraviolet rays, “tropospheric” or “ground-level” ozone is mainly man-made. In fact, when people throw around the word “pollution,” what they’re probably talking about is ground-level ozone, which is created by a chemical reaction between nitrogen oxides (highly reactive gases produced by burning fuels) and volatile organic compounds (organic compounds that easily evaporate under normal environmental conditions and can be found in vehicle exhaust as well as scented personal care products like deodorants, lotions, and bug sprays), plus sunlight. This chemical reaction usually occurs when cars, refineries, power plants, and other industrial sources emit pollutants into the environment during a hot, clear day. You probably know the result by its other name: smog.
Ozone is a climate issue not just because it is yet another concerning consequence of burning fossil fuels. According to some estimates, high levels of ground-level ozone pollution could grow in frequency by three to nine additional days per year by 2050 because of the gas’s close relationship with intense sunlight and high temperatures. While ozone dissipates fairly quickly once those conditions go away, it can build up while they last. Hot days, which are increasing in the U.S., also coincide with weak winds and stagnant air — conditions that allow ozone to accumulate in one place.
When the temperatures start to rise, here’s what you need to know and what you can do to protect yourself and others from ozone pollution.
Different pollutants cause concern at different concentrations. The Air Quality Index is designed so that, in theory, a level of “100” corresponds to the point at which people in sensitive populations might start to be affected by the pollutant in question. (To learn more about how the AQI is calculated, you can read our explainer here).
That said, “The evidence has clearly been increasing that lower levels of ozone — levels well below the current standard of 70 parts per billion — are causing more health impacts,” Katherine Pruitt, the national senior director of policy at the American Lung Association, which is campaigning to strengthen the standard to 55 to 60 parts per billion, told me.
As Pruitt explained, ozone is a caustic irritant and can corrode metals. Breathing it in can cause inflammation in anyone, “from vulnerable children and elders to even the fittest elite athletes,” Pruitt said, adding that it is, “at some level, like getting a sunburn on your lungs.” Anyone who spends time outside is vulnerable to ozone, but the more sensitive groups — including children; the elderly; people with asthma, chronic heart disease, and other diseases; and pregnant women — are at a higher risk. They might already be paying more attention to the AQI levels in their area, and will potentially notice that they need to slow down and limit exertion during “yellow” or “orange”-level ozone events.
In the short term, ozone pollution can cause coughing, shortness of breath, and a lowered immune response, on top of aggravating any preexisting lung conditions or diseases. But Pruitt stressed to me that “living in places that have high levels of ozone day in and day out, for months and years, can cause respiratory diseases, nervous system disorders, metabolic disorders, reproductive problems, and mortality. It’s not just a cough and a wheeze on one bad air day.”
Ozone requires two main ingredients: the burning of fossil fuels and other chemicals, and sunlight. While ozone concentrations can be high in communities with a lot of industry and freeways nearby, ozone is “not really so much a roadway problem; it’s more of what we call an ambient air pollutant,” Pruitt said. Ozone can travel far away from where it was produced, in other words.
There are some rules of thumb, though. The places with the highest emissions and most appropriate atmospheric conditions for ozone pollution are “increasingly the western U.S. and the Southwest,” Pruitt said. The top four worst cities for ozone on the 2024 State of the Air report by the ALA were all in California, led by Los Angeles and Long Beach.
Since the passage of the Clean Air Act in 1963, other regions of the country have been doing much better, including the Southeast, mid-Atlantic, and Northeast. (Bangor, Maine, had the cleanest air in the report.)
Because ozone is so strongly related to sunlight, it does not cause indoor air pollution to the same extent as wildfire smoke(which, if you’re keeping score, is a PM2.5 pollutant). “Because it’s so reactive, it gloms onto your furniture and your walls and stuff, once it gets inside,” Pruitt said of ozone. To protect yourself, you can just stay indoors and run your air conditioner.
But what if you want or need to go out? Because ozone is a gas rather than a particle, HEPA filters and face masks won’t protect you. Instead, Pruitt said that you can time your errands, tend to your garden, and exercise when the sunlight is the weakest — mornings, especially, tend to be less demanding on the lungs during ozone events.
The Clean Air Act of 1963 requires the Environmental Protection Agency to review the national ambient air quality standards for ozone (as well as several other pollutants) every five years. “It almost never actually does it every five years” though, Pruitt said. “Sometimes advocates have to sue them to get them to move things along.” The EPA completed its last review in December 2020, with the Trump administration maintaining the 70 parts per billion standard set in 2015. Attacks on the Clean Air Act would likely resume if Trump retakes office.
Aside from agitating for stricter clean air standards, there are measures you can take to protect others from ozone events. The simplest is not to contribute any more nitrogen oxides and volatile organic compounds to the environment than you otherwise have to when ozone levels are high. Avoid driving or idling your car; top off your tank during the coolest parts of the day, such as after dark; minimize your electricity use; and set your air conditioner no lower than 78 degrees.
In the long term, reducing ozone pollution will mean “choosing greener products for cleaning and personal care, so that we’re not producing volatile organic compounds,” Pruitt told me. The National Oceanic and Atmospheric Administration previously found that in New York City in 2018, “about half” of the ambient volatile organic compounds it measured were produced by people, not vehicle exhaust. (Here’s a guide to reducing VOCs from your rotation.)
Additionally, “transitioning to zero-emission technologies so we're not burning fossil fuels” will help limit ozone pollution, Pruitt said. The difference can be pretty significant: A study from the University of Houston published earlier this month found that by switching to electric vehicles, New York and Chicago could prevent 796 and 328 premature pollution-related deaths per month, respectively. Counterintuitively, the study found that more EVs on the roads could increase mortality in Los Angeles due to a corresponding increase in secondary organic aerosols caused by complicated dynamics between nitrogen oxides and volatile organic compounds and the city’s unique geography. “This underscores the need for region-specific environmental regulations,” the authors said.
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The company managed to put a positive spin on tariffs.
The residential solar company Sunrun is, like much of the rest of the clean energy business, getting hit by tariffs. The company told investors in its first quarter earnings report Tuesday that about half its supply of solar modules comes from overseas, and thus is subject to import taxes. It’s trying to secure more modules domestically “as availability increases,” Sunrun said, but “costs are higher and availability limited near-term.”
“We do not directly import any solar equipment from China, although producers in China are important for various upstream components used by our suppliers,” Sunrun chief executive Mary Powell said on the call, indicating that having an entirely-China-free supply chain is likely impossible in the renewable energy industry.
Hardware makes up about a third of the company’s costs, according to Powell. “This cost will increase from tariffs,” she said, although some advance purchasing done before the end of last year will help mitigate that. All told, tariffs could lower the company’s cash generation by $100 million to $200 million, chief financial officer Danny Abajian said.
But — and here’s where things get interesting — the company also offered a positive spin on tariffs.
In a slide presentation to investors, the company said that “sustained, severe tariffs may drive the country to a recession.” Sounds bad, right?
But no, not for Sunrun. A recession could mean “lower long term interest rates,” which, since the company relies heavily on securitizing solar leases and benefits from lower interest rates, could round in the company’s favor.
In its annual report released in February, the company mentioned that “higher rates increase our cost of capital and decrease the amount of capital available to us to finance the deployment of new solar energy systems.” On Wednesday, the company estimated that a 10% tariff, which is the baseline rate in the Trump “Liberation Day” tariffs, could be offset with a half percentage point decline in the company’s cost of capital, although it didn’t provide any further details behind the calculation.
Even in the absence of interest rate relief, a recession could still be okay for Sunrun.
“Historically, recessions have driven more demand for our products,” the company said in its presentation, arguing that because their solar systems offer savings compared to utility rates, they become more attractive when households get more money conscious.
Sunrun shares are up almost 10% today, as the company showed more growth than expected.
For what it’s worth, the much-ballyhooed decline in long-term interest rates as a result of Trump’s tariffs hasn’t actually happened, at least not yet. The Federal Reserve on Wednesday decided to keep the federal funds rate at 4.5%, the third time in a row the board of governors have chosen to maintain the status quo. The yield on 10-year treasuries, often used as a benchmark for interest rates, is up slightly since “Liberation Day” on April 2 and sits today at 4.34%, compared to 4.19% before Trump’s tariffs announcements.
On solar growth, Hornsea 4, and Rivian deliveries
Current conditions: The first cicada broods have begun to emerge in the Southeast as soil temperatures hit 64 degrees Fahrenheit• Hail and even snow are possible across parts of Spain today • Forecasters have identified a risk zone for tropical storm development in the Atlantic basin, with potential for the first named storm of the year to form by mid-May.
1. Global solar market expected to slow in 2025
The global solar market is expected to grow only 10% in 2025, down from 33% growth in 2024 and 87% growth in 2023, according to a new report by SolarPower Europe. The firm’s “most realistic scenario” accounts for the natural slowdown in development after a boom caused by high energy prices in 2022 and 2023, as well as the “uneven distribution of solar market growth” worldwide, with China accounting for 55% of the market share, lending to the dip in overall solar as it implements reforms this summer in how its renewables are priced and traded.
Speaking at the opening of the Intersolar 2025 conference in Munich on Wednesday, Abigail Ross Hopper, the CEO of the Solar Energy Industries Association, echoed some of the uncertainty expressed in SolarPower Europe’s report. “I don’t think any of us could be in this business if we weren’t optimistic,” she said, adding, “I think we’re going to weather through this storm, but it is going to be a bit rocky for a few years.” SolarPower Europe’s report, meanwhile, anticipates “likely” growth from 2 terawatts of global installed solar capacity at the end of 2024 to 7.1 terawatts of total installed capacity by 2030, which would meet “nearly two-thirds of the 11 terawatt renewable energy target set at COP28.” Under ideal conditions, solar could even quadruple capacity to more than 8 terawatts by the decade’s end. Read the full report here.
2. Orsted cancels 2.4-gigawatt offshore wind project in the UK, citing rising costs
The Danish energy company Orsted announced this week that it is canceling its Hornsea 4 offshore wind project in the UK due to rising supply chain costs and other “adverse macroeconomic developments,” the Wall Street Journal reported Wednesday. Hornsea 4 was expected to become one of the biggest offshore wind farms in the world, with a capacity of 2.4 gigawatts once it was completed. (Equinor’s recently paused Empire Wind I project, south of New York’s Long Island, would have had an 810-megawatt capacity by comparison.)
Orsted warned it would take a hit from the cancellation, with breakaway costs estimated to be between $533 million and $685 million. Nevertheless, “Orsted said the project no longer made economic sense, even with a contract to sell power at government-guaranteed prices for 15 years,” Bloomberg writes. Significantly, the canceled project will also hurt the UK’s efforts to add more renewables to its power grid.
3. ICYMI: Rivian lowered its delivery estimate by as much as 15% due to tariffs
Rivian beat Wall Street’s first quarter estimates, the automaker shared in its earnings letter to investors on Tuesday, but lowered its target for 2025 vehicle deliveries on account of tariffs, CNBC reports. Though the company builds all its electric vehicles in Illinois, “The current global economic landscape presents significant uncertainty, particularly regarding evolving trade regulation, policies, tariffs, and the overall impact these items may have on consumer sentiment and demand,” Rivian said by way of explanation. While it previously estimated it would deliver between 46,000 and 51,000 units in 2025, the revised outlook anticipates 40,000 to 46,000 deliveries. Last year, the company delivered just over 51,500 vehicles, Inside EVs notes.
The company also said it expects to take on “a couple thousand dollars” in additional expenses per vehicle due to the trade policies, though founder and CEO R.J. Scaringe said it’s not planning to increase the $45,000 starting price of the R2 as a result. Despite the continued uncertainty, Rivian said it still expects to achieve a “modest positive gross profit” in 2025.
4. Republicans sneak sale of public lands into reconciliation bill
Republicans on the House Committee on Natural Resources added an eleventh-hour amendment to their portion of the budget package late Wednesday night, calling for the sale of thousands of acres of public lands in Nevada and Utah. Introduced by Representatives Mark Amodei of Nevada and Celeste Maloy of Utah, the provision capitalized on longtime aspirations by Republicans to privatize Bureau of Land Management acreage in the West.
As I wrote on Wednesday, the Republicans’ maneuver, “which came at nearly midnight, left many Democrats and environmental groups deeply frustrated by the lack of transparency,” and critics had little time to comb through the extent of the proposal. While early reviews of the bill estimated the sell-off of about 11,000 acres of land, much of it apparently near cities — in keeping with Republican Senator Mike Lee’s aspirations to use BLM land for suburban sprawl — the Wilderness Society informed me last night that the accounting may end up as high as 500,000 acres or more. That’s consequential not just for public land advocates, but also because “turning over public lands to states — or to private owners — could ease the way for expansive oil and gas development, especially in Utah, where there are ambitions to quadruple exports of fossil fuels from the state’s northeastern corner,” I note in my piece. Moreover, “Reducing BLM land could also limit opportunities for solar, wind, and geothermal development.”
5. Thinning forests to reduce wildfire danger could also mitigate droughts: study
Thinning forests is a favorite idea of Republicans, who’ve rebuked blue states over forestry practices they claim exacerbate the dangers of wildfires. Now, a new study from researchers at the College of Agriculture, Biotechnology & Natural Resources at the University of Nevada, Reno looking at the hydrology of the Sierra Nevadas has found that the practice — along with prescribed fires — could also have potential upsides during drought years, including generating more mountain runoff.
According to the findings published in the journal Water Resources Research, water yields in forests thinned to densities closer to those of a century ago can be increased by 8% to 14% during drought years. That water would be “particularly valuable … to farmers and cities in central California and northern Nevada who rely on Sierra [Nevada] snowpack for much of their water supply,” according to a press release about the research. Significant flooding risks did not appear to increase with the water yields. As earlier researchers have found, however, the results of forest thinning treatments also depend on how, where, and to what extent the treatments are applied. Not all landscapes would necessarily benefit from such regimes. For example, while President Trump blamed the January fires in Los Angeles on poor forest management in California, the blazes were in chaparral, not in forests where thinning could be applied.
Riverside Clean Air Carshare
University of California, Riverside announced Wednesday that it is launching the nation’s only hydrogen-powered carshare program in a partnership with city and state agencies. Participants can rent Toyota Mirai sedans through a smartphone app and pay hourly rates competitive with Uber and Lyft fees.
Republicans Mark Amodei of Nevada and Celeste Maloy of Utah introduced the measure late Tuesday night.
Late last week, the House Committee on Natural Resources released the draft text of its portion of the Republicans’ budget package. While the bill included mandates to open oil and gas leasing in Alaska’s Arctic National Wildlife Refuge, increase logging by 25% over 2024’s harvest, and allow for mining activities upstream of Minnesota’s popular Boundary Waters recreation area, there was also a conspicuous absence in its 96 pages: an explicit plan to sell off public lands.
To many of the environmental groups that have been sounding the alarm about Republicans’ ambitions to privatize federal lands — which make up about 47% of the American West — the particular exclusion seemed almost too good to be true. And as it turned out in the bill’s markup on Tuesday, it was. In a late-night amendment, Republican Representatives Mark Amodei of Nevada and Celeste Maloy of Utah introduced a provision to sell off 11,000 acres in their states.
The maneuver, which came at nearly midnight, left many Democrats and environmental groups deeply frustrated by the lack of transparency. “The rushed and last-minute nature of this amendment introduction means little to no information is available,” including “maps or parcel information, amendment text, CBO Score, etc.,” the Southern Utah Wilderness Alliance said in a statement Wednesday.
House lawmakers appeared still to be at odds during a Wednesday morning press conference to announce the creation of a Bipartisan Public Lands Caucus. Rather than putting on the united front suggested by the working group’s name, former Secretary of the Interior and Montana Republican Ryan Zinke argued in defense of the amendment, saying, “A lot of communities are drying up because they’re looking to public land next door and they can’t use it.” Michigan Democrat Debbie Dingell then took the mic to say, “I would urge all of us that the hearings — it’s not done in the dead of night, and that we have good, bipartisan discussions with everybody impacted at the table.”
Despite the cloak-and-dagger way Republicans introduced the amendment, there are several clues as to what exactly Amodei and Maloy are up to. Republican Senator Mike Lee of Utah has aggressively pushed for the sell-off of public lands, including introducing the Helping Open Underutilized Space to Ensure Shelter (HOUSES) Act, which would “make small tracts of [Bureau of Land Management] land available to communities to address housing shortages or affordability.” Critics of the bill have called it the “McMansion Subsidy Act” and have argued — as the Center for Western Priorities’ Kate Groetzinger, does — that it would “do little to address housing issues in major metros like Salt Lake City and the fact that the current housing shortage is due largely to a lack of home construction, not land.” The Center for Western Priorities also contends that it “contains very few restrictions on what can be built on federal public lands that are sold off under the program.” Notably, Lee and Maloy have worked closely together in the past on transferring federal land in Utah to private ownership.
The land singled out in the Tuesday amendment includes BLM and Forest Service parcels in six counties in Utah and Nevada that “had already been identified for disposal by the counties,” Outdoor Life notes. While some land would be sold with “the express purpose of alleviating housing affordability,” the publication notes that “other parcels, including those in southern Utah, don’t have a designated purpose.” As Michael Carroll, the BLM campaign director for the Wilderness Society, warned E&E News, it’s in this way that the bill appears to set “dangerous precedent that is intended to pave the way for a much larger scale transfer of public lands.”
While many Republicans contend that states can better manage public lands in the West than the federal government can (in addition, of course, to helping raise the $15 billion of the desired $2 trillion in deficit reductions across the government to offset Trump’s tax cuts), such a move could also have significant consequences for the environment. Turning over public lands to states — or to private owners — could ease the way for expansive oil and gas development, especially in Utah, where there are ambitions to quadruple exports of fossil fuels from the state’s northeastern corner.
Reducing BLM land could also limit opportunities for solar, wind, and geothermal development; in Utah, the agency has identified some 5 million acres of public land, in addition to 11.8 million acres in Nevada, for solar development. While there are admittedly questions about how much renewable permitting will make it through the Trump BLM, it’s also true that solar development wouldn’t necessarily be the preference of private landowners if the land were transferred.
Tuesday’s markup ultimately saw the introduction of more than 120 amendments, including a Democratic provision that would have prohibited revenue from this bill from being used to sell off public lands, but was easily struck down by Republicans. In the end, Amodei and Maloy’s amendment was the only one the committee adopted. Shortly afterward, the lawmakers voted 26-17 to advance the legislation.