At the beginning of COVID-19 lockdowns in late March and early April, photos of clear skies and sparse freeways graced social and news media.

Twitter users lauded the pandemic as a green holiday, saying that the world, on lockdown, was allowing nature to reset, reversing climate change and revealing that humans were the true virus all along.

A report by Carbon Brief in April revealed that the pandemic was on track to reduce global CO2 emissions in 2020 in the greatest yearly decline on record.

Although things have not necessarily gone back to “normal,” many people are leaving home and traffic has increased.

A slow return to normal also includes a return to smog.

The infamous smog in Los Angeles is a form of air pollution. In an interview with Annenberg Media, Adrian Martinez, a staff attorney in the Right to Zero campaign at Earth Justice said that the vast majority of air pollution — upwards of 80% — comes from mobile sources.

World climate change is largely based on greenhouse gas emissions like carbon dioxide or methane. With some exceptions, regardless of where greenhouse gases are emitted, the effect on the environment is global.

Air pollution, on the other hand, has more of a local or regional impact. Air pollution emitted in the L.A. area mostly stays within the L.A. area. “A lot of our greenhouse gas pollution comes from cars and the gridlock that we see in Los Angeles,” Martinez said.

Whether you’re talking about greenhouse gas emissions or air pollution, cars do play a big role. The smog problem is deeper than just cars, though — it includes the entire transportation industry. The trucking, air and locomotive industries are huge contributors to pollution too.

USC Professor Edward Avol is a USC Professor of Clinical Preventative Medicine. He specializes in the respiratory effects of airborne pollutants.

It is challenging to replace these vehicles since they are large investments, he said. For example, a new locomotive, the engine that pulls a train, is a million-dollar purchase or more. As such, there are 50-year-old locomotives still on the rails.

The same goes for trucks, which are more expensive than cars and stay on the roads for many more years. The turnover of getting newer, more fuel-efficient trucks into a fleet and retiring the old ones is slow.

Diesel, for example, is a toxic air contaminator. Trucks, ships, trains, etc. that run on diesel engines impose a lot of harm to people who live near places where they are concentrated. The L.A. region has the two busiest shipping ports in the nation.

While newer cars have cleaner operating systems, mild weather in Los Angeles means that older cars are able to stay on the road much longer than they would in other parts of the country.

Governor Gavin Newsom recently signed an executive order to phase out gas and diesel-powered cars by the year 2035 in the state of California. If California were a country, it would be the fifth-largest economy in the world, so car manufacturers have reason to cater to California regulations.

Avol cautioned that renewable energy, like electric vehicles or fuel cell-based vehicles, is not a panacea. It still takes energy to create that vehicle. Once built, the power to charge those cars typically comes from a solar cell power plant. Solar cells are made of a lot of different chemicals and elements, some of which are toxic.

Mining for solar cells is a much better choice than mining for oil or coal or gas, but the net environmental footprint in the lifecycle of an electric car is not zero. It’s not a perfect solution, but it’s a step in the right direction, Avol said.

A way for individuals to mitigate emissions from transportation is through public transit. But L.A. was already largely a public transportation averse city before the COVID-19 pandemic hit. The city’s infrastructure was designed to prioritize cars, and L.A. public transit ridership was on the decline prior to the 2020 coronavirus. Now, with inherent sanitation issues on public transit, people could be even more hesitant than before to transition to commuting on buses or trains.

However, the pandemic has also shown that many people can telecommute to work from their computer, saving trips into the office.

Different neighborhoods in L.A. have varying levels of air quality. University Park sits very close to Downtown and the Harbor Freeway, where there are large-scale emissions from heavy congestion in the morning, evening and much of the day.

Avol himself grew up in Los Angeles and says the air is far cleaner now than when he was a child here. He called it, “a tremendous success story,” but also that “it’s not clean by any means yet.”

Both Los Angeles and the state of California violate the Federal Government’s Clean Air Act for at least two of the several listed pollutants –– PM2.5 and Ozone (O3). California is one of the few states that has its own state standards as well and L.A. violates the PM2.5 and O3 standards, which are equally or more strict than the Federal standards.

The American Lung Association reports every year that many cities in California are in the top 10 year after year of cities that exceed national standards of amount of particulate matter 2.5 (PM2.5), which is small, inhalable pieces of dirt floating in the air.

Females' lungs continue to develop from birth through age 16-18 while males' lungs develop through their early 20s, Avol said, meaning many students' lungs are still growing during their time in college. Exposure to heavy pollution during the developmental phase can stunt lung growth.

During growth, organ systems are sensitive to external effects, so if a child moves to a more polluted or less polluted area, studies have shown that within a year, their lung growth rates decrease or increase respectively. So, the rates are changeable during growth, but we have no information to suggest that they ever “catch up.”

However, college-aged lungs, like those in USC students, exposed to heavy pollution cannot catch up on missed growth once past the developmental stage.

“We need to get everyone to think about these sorts of issues because they do affect our health,” Avol said. “Today, tomorrow and our children’s health.”

Avol believes that the responsibility for mitigating climate change, “squarely and strongly rests on the individual.”

“If we don’t say anything, we don’t do anything,” he said."I think that most industries will not voluntarily necessarily respond in a totally responsible way. They’ll respond in a way that meets the needs of their shareholders and their bottom line."

It’s okay for those companies to make money, Avol said, because they create jobs vital to the economy, but they need to do it in a way that is responsible to the environment and public health.

“I think it does come down to us, which is timely because we have an election coming up.”

Martinez, too, thinks that large corporations play a big role in contributing to or mitigating climate change.

“While individuals also need to do their part and it’s very important,” he said, “I think the corporations often get a pass and, especially under this current federal administration, they’ve gotten a pass on cleaning up for a long time.”

A digital clock facing Union Square in New York City was recalibrated for a one-week by artists Gan Golan and Andrew Boyd for a Climate Week installation to display the time remaining before it is too late to save the earth from the effects of climate change, along with messages like “The Earth has a deadline.” But the clock’s countdown shows seven years, not the 15 before Gov. Newsom’s electric car order goes into effect.

Avol, though, is skeptical of such countdowns and does not know how exactly the artists determined that 2028 would be the point of no return.

“Some of this is no longer an issue of how do you reduce or how do we mitigate,” he said. “Some of this now is how do we adapt? I mean, these changes are in play. We cannot put the genie back in the bottle.”

He said this not with the intention to instill fear, but rather to suggest that in seven years it will not be “too late.”