While swimming laps the day before yesterday outside at Highland Park, I didn’t notice anything particular about the air I was gulping. Likewise, when I drove back to the Vintage Center to hang out with Dad, there may have been something about the air in retrospect but I didn’t note it at the time. But by the time we left a couple of hours afterwards at 3pm, a yellow haze blanketed the city, obscuring buildings just a few blocks away. Someone else leaving with us speculated that it was debris from the implosion of the Commercial Street Bridge earlier, or smoke form the Canadian wildfires.

I knew that they were replacing the bridge, that the contract provides bonuses for finishing the work early and penalties for going beyond schedule, that the scheme involves a clever slide of the already constructed replacement bridge. How could I not know? The Parkway East is shut down before and after the Squirrel Hill Tunnel, redirecting all of those cars through the East End. I braced for bumper-to-bumper traffic in my neighborhood, because that corridor can get jammed, especially during rush hour. However, they reprogrammed the lights to go longer, including an extended green on the left from Penn to Fifth, so the major arteries actually flow more smoothly now. In my opinion, they should permanently eliminate the stuttering green lights in Oakland driving east from the cathedral to Shadyside. I suspect these were intended to prevent speeding, but unfortunately the effect is to slow traffic to half the legal speed limit, frustrating drivers, and wasting time and petroleum. One downside is that the capillary streets feeding in can get backed up, especially the left turn from Craig to Fifth near my parents’ place.

While I knew about the construction, I didn’t know the timing of the detonation of the old bridge — I would have expected them to have accomplished that a little sooner, rather than on the sixth day of closing the highway. Anyhow, I figured the bad air that afternoon at 3pm couldn’t possibly have been particulates from the demolition. 376 is too far way, the event happened hours ago, and I thought the firm doing the work would mitigate dust by spraying with water afterwards (although I don’t actually know if that happened here).

Yet somehow I didn’t know about the Canadian wildfires this year. How could I have not known until the evidence was right before my eyes, and entering my lungs? How could I not have anticipated this, which I have observed before as a snowbird?

For the past couple of nights, I kept the house shut tight, in place of my ritual of throwing open the windows and closing them in the morning. Usually I have the house respiring rhythmically during the summer, circulating cool dark air, then holding its breath during the day. Instead, I turned on the air filter.

…

On the Fourth I took the busway down to Point State Park for the fireworks. I had not intended to go because of the extended heat wave, but to my surprise it broke that afternoon, while I was attending the biweekly Spanish language Meetup at Whole Foods. Two weeks later, we’re towards the end of another heat wave. Smoke and heat.

I had seen fireworks downtown several times during First Night, but this was only my second time seeing them at the Point. Maybe fifteen Julys ago, before my colleague Susie artfully arranged for close proximity shows for CMU’s pre-college programs, I once took a yellow school bus downtown with the students and our older child. I can still remember the weight on my shoulders as we both gazed at the sky. And I remember, once upon a time, as I carried our younger child up the steps to the front door at the end of a long drive home and then up the stairs to his bed, I said to my wife: There will be a last time when we hold them like this.

Now they are launching. Fireworks in the sky.

The show, billed as the largest in Pittsburgh’s history, was spectacular. I thought there were going to be drones too, but instead it was an old-fashioned pyrotechnic display. I remembered others throughout my life — at Olin Sams’ farm when a spark fell into my eye, at a grandstand in Ithaca, on a hillside in Providence, on Patriots’ Day in a taxi along the Charles, in a field in Santa Fe on New Year’s Eve of the new millennium, on Roosevelt Island looking towards the Statue of Liberty, from a hotel balcony in Louisville before the Derby.

Los fuegos artificiales. In high school the jokers would say chemistry was for those interested in explosives and drugs. I loved it anyhow, it made sense of the world. Geometry was fun for its proofs, French for new perspectives, English for building with words.

…

The crowd spontaneously sang “The Star-Spangled Banner” as the first shells launched from the river barges. The American sense of defiance, we call it the day of independence, but the emotional undercurrent is resistance, and the fireworks I love are cousins to the bombs we drop. At some point the crowd broke into shouts of “USA! USA!” for a half-minute, delighting the South Asian Indian family near where I stood, but I was a little embarrassed for being in midst of the World Cup red card fiasco.

I used to believe that fireworks would explode in outer space, that it would be easy to create a spectacle out there. After all, a shell is a packet that incorporates the fire triangle of heat (to overcome activation energy), fuel (aka reducing agent or electron donor), and oxidizer (aka oxidizing agent or electron acceptor). The oxygen in the atmosphere seemed irrelevant.

It’s more complicated than that, as I found after pulling vacuum and attempting to ignite gunpowder a decade ago with Matt and his students. It’s true that an atmosphere containing oxygen isn’t strictly necessary, because potassium nitrate (saltpeter) is present as an oxidizer. However, there must be some atmosphere or other way to keep the fuel, oxidizer, and heat in adequate contact with each other. The mean free path on Earth at sea level is a fraction of a micrometer, but on the Moon a particle typically travels kilometers before meeting another in the lunar atmosphere. The air on Earth forces fuel and oxidizer particles to collide with each other, as well as prevents heat from dispersing too rapidly. It’s rocket science.

The finale was amazing, I have never experienced one like it before. Not just their brightness and colors. I could feel the concussive shocks deep in my chest, the heat on my face.

I was in middle school the first time I visited the Point, on a field trip from my small town in Ohio. The fountain was relatively new at the time, having opened in 1974, and my teachers remarked they hadn’t seen it before. The little things we remember, I lost my Snoopy comb on that bus. And I remember we were riding around Pittsburgh and someone called out, “Hey, look, there’s a black person!” Nearly everyone of my classmates rushed to the windows on the right of the bus, pressing the glass. Only Jeanette and I stayed seated, looking at each other. The shock must have been apparent on my face, the heat in my chest.

Light and heat. Smoke and ash.