Inhalation

You begin in a wall. PVC siding, which is vinyl, which is long chains of chlorine and carbon and hydrogen that held their shape for eleven years on the south face of a house at the edge of a national forest, and when the fire arrives on forty-mile-per-hour winds through grass that hasn't seen rain since March the wall doesn't melt so much as come apart, the polymer chains cracking at 300°Cand releasing hydrogen chloride gas, and at higher temperatures the chlorine finds organic fragments in the flame and bonds with them in the exact configuration that makes a dioxin, one of the most persistent and carcinogenic molecular structures humans have ever measured, and you are adsorbed to the surface of a carbon particle that carries it, a fine black sphere of incomplete combustion roughly 2.2 microns across, smaller than a red blood cell, small enough. In the same fire and the same sixty seconds the polyurethane foam inside the couch decomposes into isocyanatesand hydrogen cyanide and benzonitrile, and the pressure-treated deck out back, chromated copper arsenate forced into the wood grain under industrial pressure in 2001, releases its arsenicin the trivalent form, the more toxic form, the form that does the most work on DNA, and the car in the garage gives up its lead and cadmium and the carpet gives up its polybrominated diphenyl ethers and every organic surface that burned incompletely produces benzo[a]pyrene, and all of it rides the thermal column upward in a plume that will travel dozens or hundreds of miles depending on wind, and the emission factorsfor these compounds run one to three orders of magnitude greater than a normal wildland fire, and for dioxins specifically five to six orders of magnitude greater, which is a hundred thousand to a million times more dioxin from a burning house than from a burning forest, and you are in that plume now, 2.2 microns of carbon and chemistry, cooling as you rise, and you are moving.

You drift. You are one particle among a hundred thousand per cubic centimeter in the near-field plume and as the plume disperses you become one among thousands then hundreds then tens but you do not settle, you are too small to settle, gravity barely registers at your scale, and you remain suspended for days or weeks, carried on prevailing winds across a landscape where eventually a woman opens a door and steps outside and breathes in and you enter on that breath. The air velocity in the nostril is roughly four meters per second during normal inhalation, faster during the sharp intake of someone who has just stepped into smoke, and the nasal turbinates, three curved shelves of bone wrapped in mucous membrane, create turbulence meant to slam larger particles into the sticky mucosal surface where they'll be trapped and swallowed or blown out, but they were built for particles ten or fifty times your size and you pass through the turbulence without touching anything and you descend past the pharynx and the larynx into the trachea where the mucociliary escalator begins, two hundred cilia per cell beating ten to twenty times per second in coordinated waves that move a blanket of mucus upward at one millimeter per minute, a slow persistent conveyor carrying trapped particles up and out of the lungs and into the throat to be swallowed, and this system works, it works beautifully for particles that land on it, but you don't land on it, you are suspended in the airstream flowing past the mucus layer and you follow that airstream as the trachea branches into bronchi and the bronchi branch into bronchioles and the bronchioles narrow and narrow until the ciliated cells disappear entirely and there is no more escalator, there is no more defense except the alveolar macrophages waiting at the end of the passage, single cells whose whole job is to engulf foreign particles through phagocytosis, and they extend pseudopods toward you, but their efficiency drops as particle concentration increases, their phagocytic index falling measurably with each wave of smoke-borne particulate, and the macrophages that do manage to engulf particles become inflamed and dysfunctional, releasing cytokines that summon more immune cells that create more inflammation that damages the tissue they were supposed to protect, and now you are at the alveolar wall, the last boundary, a membrane roughly half a micron thick, thinner than you are wide, separating air from blood, and you settle onto its surface and the epithelial cells take you in through caveolin-mediated transcytosis, the caveolin proteins forming a pit in the cell membrane that deepens into a vesicle that carries you through the cell's interior and releases you on the other side into the capillary blood and the blood goes everywhere, it reaches every organ in under a minute, and you are standing at the kitchen sink with a glass of water and you don't feel anything because there is nothing to feel at this scale, no sensation that corresponds to what just crossed into you, and the dioxins adsorbed to the particle's surface are already activating aryl hydrocarbon receptors in your endothelial cells and the benzo[a]pyrene is being metabolized by your own cytochrome P450 enzymes into BPDE, benzo[a]pyrene 7,8-diol-9,10-epoxide, which binds covalently to your DNA and forms adducts, bulky molecular lesions that distort the double helix at the point of attachment, and your cells have repair mechanisms for this, you have a gene called OGG1 that excises oxidized bases and a gene called MGMT that removes mutagenic adducts, but the particulate matter is silencing those genes through promoter hypermethylation, methyl groups added to the DNA near the repair genes' start sites that fold the chromatin closed so the genes can't be read and the repair proteins aren't made and the adducts persist through replication and when your cells divide the damage is copied, the O6-methylguanine causing G-to-A transitions, point mutations accumulating in tumor suppressors like TP53 and oncogenes like KRAS, and you are drinking your water and the arsenic from someone's deck is generating reactive oxygen species that collapse your mitochondrial membranes and the damaged mitochondria release more reactive oxygen species in a feedback loop your cells cannot outrun, and some of the particles you inhaled were caught by the escalator after all, the ones that landed in the bronchi, and the cilia did their job and swept them upward and delivered them to your throat and you swallowed them without knowing, and now they are in your stomach and your intestines and the PAHs are crossing your gut epithelium and entering your portal circulation and reaching your colon, and some of the compounds in your blood are being filtered by your kidneys and concentrating in your urine and sitting in your bladder for hours, the carcinogens pooling against the urothelial lining while you sleep, and you are sleeping now, you are asleep in your bed in a house the fire didn't reach, and your body is doing what bodies do, repairing what it can and carrying what it can't repair and dividing its cells and copying its DNA including the errors, and across the country 91,460 other bodies tracked over twelve years did the same, breathed and slept and carried what they couldn't repair, and for every additional microgram per cubic meter of wildfire smoke PM2.5 they breathed over thirty-six months their risk of lung cancer was 92 percent higher and their risk of colorectal cancer was 131 percent higher and their risk of breast cancer was 109 percent higher and their risk of bladder cancer, the organ where the carcinogens pool while you sleep, was 249 percent higher, and these findings were presented two weeks ago and have not yet been peer-reviewed and the confidence intervals were wide and the researchers were careful and none of it changes what is happening inside you right now, the repair genes working until they can't, the cells dividing until they divide wrong, and at three degrees of warming the plumes will kill 64,000 Americans per year and every ton of CO₂ emitted adds $11.20 in smoke-related mortality and probably nothing comes of this particular breath, most of the time the body holds, most of the time the corrections are enough, but the fires are not getting smaller and the smoke seasons are not getting shorter and the houses keep going up at the edges and the plumes keep carrying compounds that wildland fire alone would never produce, and you will breathe again tomorrow and you are breathing right now and so am I and the membrane is half a micron thick and it is open, it has always been open, it was never designed to close.