Georgia’s asthma rates are high – about 9.6% of adults report asthma, and the EPA warns that air pollutants (especially fine PM2.5 and ozone) trigger and worsen asthma attacks. Particles under 2.5 µm (“PM2.5”) can penetrate deep into the lungs and cause serious health problems. Children (≈6 million U.S. with asthma) and seniors are especially vulnerable to these effects, with ommon allergens (pollen, mold spores) and airborne pathogens (viruses/bacteria) acting as triggers.

MARTA carries approximately 500,000 riders per weekday, plus tens of thousands use the airport shuttle system daily. Many riders are children, the elderly, or health-compromised, making vehicle air quality a pressing public health issue.

Enclosed transit cabins tend to accumulate pollutants, and commuters in buses and trains typically inhale concentrated exhaust particles and dust. Studies show bus riders face the highest PM2.5 exposure of any transport mode – up to 3–4 times more than in cars or bikes. In practice, most Atlanta buses and rail cars have only standard filters (often MERV-8 or so). When doors open at stops, dirty ambient air floods the cabin; diesel fumes, brake dust, tire particles, and road debris slip past weak filters and recirculate inside. Without high-grade filtration or fresh-air intake, these particles and allergens linger in the air that riders breathe. Crowding and poor ventilation can also let viruses accumulate on busy routes.

MARTA operates approximately 550 buses and 296 rail cars. Most are older models whose HVAC units cannot accept high-efficiency filters. (MARTA’s new rail cars – 254 on order – will have “improved heating, cooling” systems, but deployment won’t cover the fleet for years.)

Current Efforts: MARTA spent ~$850K to add needlepoint bipolar ionization devices in 209 AC units at 18 facilities (offices, depots), which help neutralize pathogens indoors without ozone. The agency also uses aggressive cleaning and disinfectant fogging on vehicles, and is exploring UV lights and upgraded HVAC filters. However, no similar high-end filtration is in use onboard any bus or train yet.

Hartsfield–Jackson’s shuttle/van fleet (~300 vehicles) is mostly diesel and aging; a pilot of two 40-ft electric shuttles (22 pax each) was added in 2019. The Plane Train people-mover is being rebuilt with 63 new cars ($300M project) for energy efficiency, but filter upgrades on those cars have not been publicized. (By contrast, construction guidelines do mandate at least MERV-8 filtration in terminal HVAC – still well below the MERV-13 minimum recommended for health.)

Traffic pollution infiltrates transit vehicles. Every vehicle emits PM2.5 into the shared air. Traffic-generated exhaust, brake/tire wear, and resuspended road dust raise in-cabin particle levels substantially. Studies confirm that enclosed buses carry very high PM2.5 counts under normal conditions. In short, without upgraded filters, every transit ride exposes passengers to significant airborne hazards.

Evidence:

• True HEPA filters trap ≥99.97% of particles ≥0.3 µm – including pollen, mold spores, dust, vehicle soot and virus-laden droplets. The
• EPA explicitly recommends upgrading to MERV-13 or HEPA-grade filters wherever possible to reduce airborne disease and allergies.

A 2023 pilot study placed three small HEPA air purifiers inside a public bus. The units reduced in-cabin PM2.5 by 42–74%, bringing pollutant levels down to or below WHO guideline values. HEPA units outperformed the bus’s standard ventilation and kept air near-clean even with doors open at stops.

A controlled trial (children with asthma exposed to traffic pollution) showed that installing a HEPA cleaner at home significantly improved asthma outcomes. Asthma-control scores improved ~30% (from 1.3 to 0.9, P=0.003) and quality-of-life scores also rose, compared to a placebo. This demonstrates that reducing fine particles in an environment directly yields fewer asthma symptoms. Translated to transit, installing HEPA filtration inside vehicles should similarly lower attacks and wheezing on board.

By trapping particles this small, HEPA filters also catch many airborne viruses and bacteria along with pollutants. They produce no ozone or harmful byproducts (unlike some UV/ionization systems), making them safe for use around all riders.

Given the long timeline and high cost of overhauling all vehicle HVAC units to MERV-13/HEPA, portable HEPA air purifiers are a smart interim fix. 

HEPA units remove 99.97% of allergens and fine particles (PM2.5, dust, pollen, mold, smoke, viruses) from the air. (By comparison, MARTA’s current filters only block much larger particulates.) Deploying these inside cabins aligns with EPA guidance to use the highest feasible filter efficiency.

Viability:

• Small purifiers (USB or 12V powered) can be placed on floor or shelves in each vehicle.
• No HVAC modification is needed.
• Units cost only ~$25–$30 each in bulk.
• Maintenance is simple – swap filters on a regular schedule (e.g., monthly checks, replace every 6–12 months).

The bus pilot and the asthma trial prove HEPA’s impact. In practice, 2–3 purifiers per bus or train car should greatly cut passenger exposure. For example, deploying 3 units per MARTA vehicle (buses and rail cars) and each ATL shuttle aligns with the above study’s setup.

These devices are widely used in offices and homes. They produce no noise or glare, no harmful byproducts, and riders will feel reassured by cleaner air.

Cost:

Total Cost: At ~$25–30 each, even outfitting all older vehicles is very cheap:

• MARTA (~846 buses + rail cars) × 3 units = ≈2,538 units → ≈$76,000–$81,000.
• ATL shuttles (~300 vehicles) × 3 units = 900 units → ≈$22,500–$27,000.
• Grand total: ≲$110,000 (well under 0.1% of the combined MARTA and Atlanta Aviation operating budgets – roughly $652 million + $353 million).

This small outlay protects hundreds of thousands of riders. The potential public health payoff is large: far fewer asthma and allergy incidents on transit. Reduced illness would save medical costs and lost productivity. Improved passenger confidence may boost ridership. Compared to the budgets, the return is enormous.

A prudent approach is to start with a pilot (e.g., 10–20 buses and 5 trains, plus a few shuttles) to validate the air-quality gains. We expect rapid success (as the research predicts). Assuming positive results, expansion to the full fleet can follow within a year.

This plan complements MARTA’s greening efforts and ATL’s transit upgrades. It bridges the gap until all vehicles receive top-tier HVAC systems. Because it is quick, safe, and budget-friendly, it avoids delays from complex capital projects.

Call to Action: 

• Authorize purchase and installation of HEPA purifiers in all older MARTA buses, trains, airport shuttles, and Plane Train cars. (Units can be procured in bulk with federal/state transit funds.)
• Aim to pilot within 3–6 months and fleet-wide rollout within the next 12–18 months.

The data confirm that poor air in transit vehicles is a real health issue for Atlanta. Installing portable HEPA purifiers is a scientifically supported, high-impact solution. For a tiny fraction of the budget, MARTA and Hartsfield–Jackson can dramatically improve riders’ health and comfort. Thank you for your commitment to public health and your consideration of this important initiative.