It started this week.

Tree pollen counts across New York City hit moderate-to-high levels in late March and are climbing. Oak, birch, and maple are all releasing simultaneously this year — a "pollen vortex" effect that allergists have been flagging as a consequence of compressed cold seasons. If your eyes are itchy, your nose won't stop running, and your throat is scratchy in the morning when you wake up inside your apartment, you're not imagining it.

The outdoor air is one problem. The indoor air is the one most New Yorkers never address.

Here's the thing about New York housing stock: a lot of it is old.

The median age of a residential building in NYC is over 70 years. Pre-war apartments, brownstones, postwar walk-ups — these buildings were not designed with modern air filtration in mind. They have gaps, drafts, and HVAC systems that circulate air without meaningfully filtering it. Many apartments have no central air at all — just windows in summer and radiator steam heat in winter.

During allergy season, that matters more than most residents realize. Here's what's getting into your apartment whether you open the windows or not:

Outdoor pollen. It travels through window gaps, under doors, and on your clothing. A single outdoor excursion can bring significant pollen load into a small space.

Mold spores. Spring's wet weather, combined with NYC's aging building stock, creates ideal conditions for mold growth — in walls, around windows, in bathrooms. Mold spores are a major allergy and asthma trigger, often worse than pollen.

Dust mites. Year-round in NYC but worse after winter, when windows have been sealed and indoor humidity has fluctuated. Radiator heat cycles dry out and redistribute dust constantly.

Pet dander. If you have a dog or cat — and a lot of New Yorkers do — their dander is accumulating in carpets, upholstery, and bedding. Spring shedding season compounds it.

Street particulates. NYC streets generate significant fine particulate matter (PM2.5) from traffic, construction, and general urban activity. It enters buildings through ventilation and gaps. Queens, the Bronx, and parts of Brooklyn near major expressways have persistently elevated particulate levels.

The EPA has repeatedly found that indoor air quality is often 2 to 5 times worse than outdoor air quality in urban environments. For people with asthma or allergies, indoor air quality during spring and summer is a significant driver of symptom severity.

The practical impact for NYC residents:

For homeowners, poor indoor air quality during allergy season can also accelerate wear on HVAC systems that have to work harder against clogged filters and particulate buildup.

The good news: indoor air quality is a problem with practical, affordable solutions. Most of them don't require a contractor or a permit.

Change or upgrade your air filters right now. If your apartment or home has a central HVAC system, the filter should be changed at the start of allergy season — April at the latest. Switch from standard 1-inch filters to MERV 11 or higher if your system supports it. This captures pollen and mold spores that cheaper filters miss.

Add a standalone air purifier to your bedroom. Your bedroom is where you spend a third of your life. The single highest-impact thing you can do for sleep quality and allergy symptom reduction is clean the air in that room. Look for HEPA filtration and coverage appropriate for the room size. The PuroAir 240 covers up to 1,000 sq ft on a single pass — right-sized for a large NYC bedroom or open living area — and the PuroAir 400 handles up to 2,000 sq ft, which works well for open-plan apartments and homes. Both use medical-grade HEPA-14 filtration, which captures 99.99% of particles down to 0.1 microns — pollen, mold spores, dust mites, pet dander, and fine particulates.

Keep windows closed during peak pollen hours. Pollen counts are highest from 5 AM to 10 AM. If you want morning ventilation, do it after 11 AM. At night, keep windows on the windward side closed.

Wash bedding and pillowcases weekly. Pollen and dust mites accumulate in bedding faster than anywhere else in the apartment. Hot wash (at least 130°F) kills mites. Allergen-proof pillow and mattress covers are worth the investment.

Control humidity. Mold thrives above 50% relative humidity. Spring rain and poor building ventilation can push indoor humidity up. A basic hygrometer (under $15 on Amazon) tells you where you stand. If you're above 55%, a dehumidifier in the problem areas helps — especially basements, bathrooms, and rooms with window AC units.

Vacuum with a HEPA filter. Standard vacuums exhaust fine particles back into the air. A HEPA-filter vacuum captures rather than redistributes allergens. If you have carpets or pets, this matters significantly.

Beyond the daily fixes, spring is the right time for NYC homeowners to check a few things that directly affect indoor air quality:

Inspect window and door seals. Winter temperature swings crack caulking and weatherstripping. Gaps let in both pollen and rodents. Walk the perimeter of your home and seal anything that's degraded.

Check bathroom exhaust fans. These are the primary moisture and mold-control tool in NYC apartments and homes. If yours sounds labored or doesn't pull air effectively, the motor may be failing. A replacement is a $30-60 DIY project that pays off in mold prevention.

Dryer vent inspection. Clogged dryer vents are a fire risk and also a moisture source that feeds mold. If your dryer is taking longer to dry clothes, the vent probably needs cleaning.

Look for water intrusion. Spring rains reveal roof, flashing, and foundation issues. Water stains on ceilings or walls that weren't there in fall need attention before they become mold problems over summer.

Air quality data from NYC's monitoring network consistently shows elevated PM2.5 and ozone levels in the South Bronx, Southeast Queens, and areas near the BQE corridor in Brooklyn. Residents in these neighborhoods have statistically higher asthma rates — particularly children — and allergy season compounds existing respiratory stress.

If you live in one of these neighborhoods, indoor air quality mitigation is not a luxury item. It's a health measure. The cost of a solid air purifier for your bedroom is meaningfully less than an ER visit or repeated urgent care trips for respiratory flare-ups.

Spring in NYC is beautiful and brutal simultaneously. The pollen count is not something you control. Your indoor air is.

Changing your filters, adding a HEPA air purifier, and controlling indoor humidity are the three moves that make the most measurable difference in allergy season comfort and respiratory health. They're doable this weekend.

The outdoor air will sort itself out by July. Your apartment won't unless you act.

The Metro Intel covers practical NYC living — homeownership, small business, and everything in between. Have a tip or story lead? Hit reply.