Leaf blowers can make an infernal racket, and environmental officials say that exhaust from blowers and other gas-powered lawn and garden equipment is a surprisingly big source of air pollution.

But are landscaping workers who use the equipment day in and day out exposed to potentially harmful emissions? A 2006 study by the U.S. Environmental Protection Agency raised concerns, but otherwise little research exists. So FairWarning decided to commission some testing of its own.

With the help of a grant from the Fund for Investigative Journalism, FairWarning hired a workplace safety and health consulting firm, Health Science Associates of Los Alamitos, Calif. It carried out testing over three days at sites in the San Fernando Valley area of Los Angeles. A copy of the test report is available here.

The testing focused mainly on measuring ultrafine particles in the air around gas-powered machines. Although no nationally accepted occupational safety standards exist for ultrafine particles, they are a source of increasing concern among scientists. Due to their small size – about one-thousandth the width of a human hair — they can be breathed deeply into the lungs, where they are thought to raise the risk of such ailments as lung cancer and heart disease.

In all, the testing involved six landscaping workers and 16 pieces of gas-powered equipment from 818 Land Maintenance, a small Chatsworth, Calif., firm, and Gothic Landscape, a Santa Clarita, Calif.,-based company that operates in four states. Four electric machines were provided by the American Green Zone Alliance, a Studio City, Calif.,-based firm that promotes “zero-emission” landscape maintenance.

To detect concentrations of ultrafine particles, HSA’s industrial hygienists used a P- Trak, a machine about the size of a shoebox with an attached wand-like probe. Equipped with their devices, the industrial hygienists strode alongside landscaping workers as they operated leaf blowers, lawn mowers , string trimmers and a chainsaw.

In one instance on Day 1 of testing, ultrafine particle levels around a leaf blower were more than 50 times higher than at a nearby clogged intersection at rush hour. Day 2 involved retesting machines and comparing particle concentrations around the gas-powered equipment to the particle levels around electric equipment. Finally, on Day 3, a somewhat newer batch of machines – model years 2015-2017 – were tested.

The bottom line: Gas-powered machines, with only a couple of exceptions, appeared to generate substantial amounts of ultrafine particles – far more than detected at a busy intersection — while the electric machines did not.

HSA also did limited testing for benzene, a carcinogen, and noise. It found that the benzene levels were within occupational regulatory limits. The noise testing provided inconclusive results on whether regulatory limits were exceeded