Metal contents and size distributions of brake and tire wear particles dispersed in the near-road environment.

Traffic related non-tailpipe particulate matter emissions can rival the continuously decreasing tailpipe emissions in modern fleets. Non-tailpipe emissions have become the dominating source of traffic emissions in California already. This study measured ambient PM2.5 and PM10 concentrations at near road environments for two major highways in California, I-5 in Anaheim and I-710 in Long Beach. A total of 51 elements were measured from filter samples collected over four-hour intervals for a two-week period in the winter of 2020 before the statewide lockdown by the COVID-19 pandemic. Iron was the most abundant element in ΔPM10 (differences between downwind and upwind sites), contributing to 30 % and 24 % of total measured elements in ΔPM10 at the I-5 and I-710 locations, respectively. Iron correlated highly with other brake wear markers (e.g., titanium, copper, barium, manganese, and zirconium) with coefficient of determination (r2) ranging from 0.67 to 0.90 in both PM2.5 and PM10. Silicon was the second most abundant element, contributing to 21 % of total measured elements in ΔPM2.5 and ΔPM10. Silicon showed strong correlations with crustal elements such as calcium (r2 = 0.90), aluminum (r2 = 0.96), and potassium (r2 = 0.72) in ΔPM2.5, and the correlations were even higher in ΔPM10. Barium had a weak correlation with zinc, a commonly used maker for tire wear, with r2 = 0.63 and r2 = 0.11 for ΔPM10 at the I-5 and I-710 locations respectively. Barium showed a positive correlation with crosswind speed and could serve as a good brake wear PM marker. Hourly PM2.5 concentrations of iron and zinc showed cyclic peaks from 0800 to 1000 h at I-5 during weekdays. Particle mass distributions showed peaks near ~7 µm, while particle number distributions showed peaks near 2.1 µm and 6.5 µm, respectively. This is consistent with brake wear and road dust size ranges previously reported.

The effect of built-in and portable ionizers on in-cabin ozone concentrations in light-duty vehicles.

This paper investigates the effects of ionizers on the ozone concentration within vehicle cabins by using a series of measurements combined with a kinetic box model. Testing consisted of measuring ozone concentration during static tests where the ventilation of the test vehicle was turned on and off depending on the test. This testing was repeated for three different portable ionizers and two vehicles with built-in ionizers. Ionizer A produced ozone at a rate of ∼0.04 ppb s-1 (∼0.68 mg h-1), which increased the in-cabin O3 concentrations of a Mitsubishi Mirage to ∼10 ppb with the fan off and ∼6 ppb in the recirculation mode. In the fresh air mode, in-cabin O3 concentrations were dominated by outdoor-to-indoor transport. Ionizer B and C produced O3 at a rate of less than 0.008 ppb s-1 (<0.14 mg h-1); however, during retesting, ionizer C was shown to emit large amounts of ozone for short amounts of time while being tested up close. The same testing was completed on vehicles with built-in ionizers; these produced <0.01 ppb s-1 (<0.32 mg h-1 in the Buick Enclave and <0.25 mg h-1 in the Hyundai Genesis), and in-cabin O3 concentrations were again dominated by outdoor-to-indoor transport with fresh air ventilation. While ionizers are currently regulated, the negative impact they have on in cabin air quality is important to continue monitoring.

Behavior of carbon monoxide, nitrogen oxides, and ozone in a vehicle cabin with a passenger.

Drivers and passengers are exposed to high concentrations of air pollutants while driving. While there are many studies to assess exposure to air pollutants penetrating into a vehicle cabin, little is known about how individual gas pollutants are behaving (e.g. accumulating, depositing, reacting etc.) in the cabin. This study investigated the characteristic behavior of CO, NO, NO2 and O3 in a vehicle cabin in the presence of a driver with static, pseudo dynamic and dynamic tests. We found in our experiments that CO and NO concentrations increased while O3 and NO2 concentrations decreased rapidly when cabin air was recirculated. A kinetic model, which contains 20 chemical reactions, could predict the static test results well. CO and NO accumulations in the cabin were due to exhalation from the driver and conversion of NO2 to NO upon deposition to surfaces may also play a role. Pseudo dynamic and dynamic test results showed similar results. During the fresh air mode CO, NO, and NO2 followed similar trends between the inside and outside of the cabin, while in cabin O3 concentrations were lower compared to outside concentrations due to reactions with the human and surface deposition. The Cabin Air Quality Index approached 0.8 and 0.4 for O3 during pseudo dynamic and dynamic tests, respectively. Accumulation of NO in the cabin was not obvious during the dynamic test due to a large variation of outside NO concentrations. We encourage auto manufacturers to develop control algorithms and devices to reduce a passenger's exposure to gaseous pollutants in vehicle cabins.