Evaluation of Particulate Emissions During Braking Tests in Technical–Mechanical Overhaul Workshops in Armenia-Quindío (Colombia)

Abstract

Brake testing of vehicles is one of the most important tests performed in technical–mechanical overhaul workshops (TMOWs). During this test, fine and ultrafine particles are emitted, exposing workers to health risks. A mixed descriptive observational study was conducted in 10 TMOWs in Armenia (Colombia), where particle sampling was performed using the NIOSH 0600 method. One third of the samples were sent for SEM analysis to determine their chemical composition and particle size. The average occupational exposure was 24.31 mg/m³, almost 10 times higher than the threshold limit value for ultrafine particles. The range of particle sizes was from 1.12 to 54.33 µm, with an arithmetic mean of 14.89 µm. The ultrafine size ranged from 198 nm to 798 nm. Traces of components of refractory materials, fiberglass, wollastonite, and thermoplastics, among others, typical of brake pads, were found. This research allows us to confirm the presence of fine and ultrafine particles in TMOW brake tests. Therefore, we recommend improvement actions based on epidemiological surveillance programs of the respiratory health of workers.

1. Introduction

Particulate emissions that do not come from combustion vehicle exhaust (NEEs—non-exhaust emissions) are particles released into the air due to brake wear, tire wear, road surface wear, and road dust suspension.

Techno-mechanical revisions are mandatory in Colombia from the sixth year after the purchase of the vehicle. In these inspections, many safety elements of the vehicle are checked by means of tests, among which the brake test is one of the fundamental ones. It is performed on all categories of vehicles: light, heavy, motorcycles, trailers, etc. The brake test is performed on a brake tester, which is a machine that simulates rolling on asphalt by means of rollers. The brake tester analyzes the vehicle’s braking efficiency, i.e., the relationship between the braking forces in relation to the vehicle’s weight and the imbalance, i.e., the difference in braking forces between the wheels on the same axle. This test is performed on both the front and rear axles. The braking test is performed at a speed of approximately 5.5 km/h and simulates rolling on asphalt [1]. There are also very few studies showing the presence of nanoparticles between 1.3 and 10 nm in NEE emissions from vehicle braking [2].

Although this is a progressive test, i.e., there is no sudden braking and it is carried out at a minimum speed, some wear of the brake and tire material in contact with the rollers cannot be ruled out, especially in the case of heavy vehicles. And this wear eventually results in the emission of NEE particles into the shop air [3]. Since technical–mechanical overhaul workshops (TMOWs) are generally confined and sometimes poorly ventilated spaces, the concentration levels of particles emitted inside an TMOW can exceed the levels found in the outside air. As a result, workers who spend their entire working day in these spaces may be at risk of inhaling particles without even knowing it.

In a comprehensive review of NEE emissions from brakes [3], it was found that brake wear is recognized as one of the important sources of NEEs, with a relative contribution to these emissions ranging from 16 to 55%. In addition, it is estimated that about 50% of the total brake wear is emitted to the air as PM10 at 2 to 8 mg/km. The remainder may be deposited on the road or in the immediate vicinity or may be drawn in by the vehicle. Trace amounts of Cu–Sb in a 5:1 ratio have also been found.

Tire wear appears to be the major contributor to the presence of Zn in the urban environment [4]. Although it is recognized that Zn is emitted during the tire wear process, its use as a tracer for tire wear particles is complicated by the presence of other sources. The absence of other metals associated with tire wear also precludes the calculation of a diagnostic ratio, as has been performed for brake wear particles.

At the international level, there is a published review of the existing environmental pollution in motor vehicle repair shops in Saudi Arabia and of the health risks to their workers [5]. However, it does not distinguish between particulate emissions from engine combustion and particles emitted during braking. On the other hand, there is a book on air quality in general, which includes a chapter on the assessment of indoor air quality in an automotive assembly plant in Malaysia [6]. However, the study is limited to the determination of PM10 emissions in the paint shop of the plant.

Other works deal with the analysis of pollutants in vehicle maintenance and repair shops [7], but they also do not study the NEEs. In Colombia, there are no studies of the NEEs from brake tests in TMOWs.

Traffic-related particulate matter plays an important role in the development of adverse health effects, including respiratory [8,9,10], cardiac [11,12,13], and kidney diseases [14], as has been widely documented in epidemiological and acute toxicity studies. There are also studies linking exposure to air pollution with adverse effects on child development [15,16], obesity [17], sclerosis [18], hypertension [19], occurrence of neurodegenerative diseases [20,21,22,23], and risk of mental illness [24,25].

Previous studies derived from the analysis of pollutant emissions have determined that pollution from NEEs can be greater and worse than that from automobile exhaust [26]. It is currently estimated that NEEs make up the majority of primary particulate matter from road transport, including PM10 and PM2.5, and are not related to exhaust emitted from road traffic [27].

Therefore, these NEEs are a serious problem that mainly affects larger and heavier vehicles, including trucks, buses, vans, SUVs, and also electric vehicles. While pollution from engines is steadily decreasing due to increasingly stringent emission regulations, it appears that pollution from tires and brakes is increasing due to the increase in the average weight of vehicles.

The objective of this research is to evaluate the emission of particles during braking tests of the Technical Mechanical Revision Workshops (TMOWs) in Armenia (Colombia), since the degree of risk of ultrafine particles to the health of TMOW workers is currently unknown at the national level.

2. Materials and Methods

A qualitative and quantitative observational descriptive study of the particulate properties of the environmental samples collected was carried out. This is a descriptive observational study because an inspection visit was made to the workplace and the characteristics of the worker’s tasks were observed in detail. This is a qualitative study because the morphology, size, and chemical composition of the particles were detailed, and it is quantitative because the mass concentration of the particles in the environment was measured in mg/m³ and the degree of danger to the worker’s health was evaluated based on the current threshold limit values (TLVs) for inhalable particles [28].

The 10 existing TMOWs in the city of Armenia, Department of Quindío (Colombia) [29], were visited and sampled, of which two were in closed environments and the rest in large, well-ventilated rooms. The TMOW areas are large in the open spaces, with areas exceeding 500 m², while the enclosed spaces do not exceed 300 m², with ventilation at the entrance and exit of vehicles.

The braking test in the TMOWs followed these typical steps [30,31]:

• The vehicle was positioned on the brake tester rollers or platform, ensuring it was securely aligned.
• Initial check: The worker verified the condition of the braking system, including brake pedal functionality and fluid levels.
• Axle testing: The brake rollers were activated for one axle at a time, gradually applying the brakes.
• Force measurement: The braking force was measured for each wheel using sensors in the rollers.
• Balance assessment: The braking forces were compared between wheels on the same axle to check for imbalances.
• Parking brake test: The parking brake was engaged and its effectiveness measured.
• Test results: The data were analyzed against regulatory standards for brake performance and efficiency.
• Final inspection: The worker verified any anomalies or faults detected during testing.
• Reporting: The worker documented and provided results to the vehicle owner, indicating pass/fail status.

In order to characterize the particles over a wide size range, a GilAir5 Gilian Multi Fol. No. 800519 air sampler pump with a Sensidyne Filian Gilibrator TM 2 803024B, Bubble Generator Rang 20 CC-6LPM P7N 800286 (SENSIDYEN, St. Petersburg, FL, USA) was used. This device was placed on the worker in charge of the braking tests.

The NIOSH 0600 analytical method [32] was used to capture ultrafine particles. The method for indoor airborne particulate sampling involved these key steps:

• A pre-weighed polyvinyl chloride (PVC) filter was placed in a cassette holder connected to the sampling pump.
• The pump was calibrated to a flow rate of 1.7 L per minute (L/min) using a primary standard.
• The sampling unit was placed in the indoor environment at breathing zone height of the worker and collected air samples for the test duration.
• The filter cassette was sealed and transported to the laboratory, ensuring no contamination or loss of particulate matter.
• In the lab, the filter was weighed to determine the total particulate collected (gravimetric analysis).
• Field blanks were used to correct for background contamination.
• Airborne particulate concentration was calculated using the sample mass, air volume, and correction factors.

Sampling was carried out in summer, during sunny and dry days, and with calm wind. The sampling time was 20 min, which was the length of the brake test per vehicle. Three samples were collected from the worker performing the brake test inside the TMOW. Likewise, 3 samples were taken from the outside air. A 37 mm cassette and a 5.0 µm PVC filter from Sensidyne lot # 51282 (SENSIDYEN, St. Petersburg, FL, USA) were used for sampling.

Particle concentration was calculated by dividing the weight of particles deposited on the filter using an analytical balance Mettler-Toledo MS105DU (Mettler-Toledo, Columbus, OH, USA) by the volume of air aspirated by the pump during the test (34 L). The accuracy of this balance is 0.01 mg for a maximum capacity of 42 g [33].

The worker had the sampling line placed as shown in Figure 1: the pump was attached to the belt of the trousers and connected to a hose attached to the particulate retention filter. The filter was placed close to the shoulder without interfering with arm movement. The pump was activated during the 20 min brake test.

For the analysis of the particle distribution, a scanning of the images was carried out in the electron microscopy laboratory of the University of Antioquia, using Scanning Electron Microscopy (SEM) with EDAX, AFM, and FTIR detectors, in order to differentiate the chemical composition of the particles and to be able to attribute their origin (engine, brakes, or tires). From the elemental compositions of the detected particles, the average normalized composition of all particles was calculated. On the other hand, the size of the particles was determined directly from the enlarged microphotographs of the filters.

3. Results

Table 1. Average occupational exposure (AOE) of the TMOWs sampled.

TMOW	AOE (mg/m3)	Outdoor Air Concentration (mg/m3)
#1	10.8	0.98
#2	5	0.58
#3	12.5	0.99
#4	100	2.5
#5	75	3.08
#6	7.5	0.43
#7	6.8	0.4
#8	6.5	0.75
#9	13.6	1.58
#10	5.5	0.3

shows the average occupational exposure (AOE) of the TMOWs sampled and the concentration of particles in the outside air. Values correspond to the mean of the 3 samples in each TMOW.

The mean AOE inside the TMOWs was 24.3 mg/m³. On the other hand, the average concentration of ultrafine particles in the outdoor air was 1.1 mg/m³ (Table 1).

The average concentration for heavy vehicle tests was 12.5 mg/m³, and a 3:1 ratio of light vehicle to heavy vehicle tests was observed.

Of the 50 samples collected at the workshops, the 10 samples with the highest concentrations were selected for SEM analysis, 5 from inside the TMOW and 5 from outside air. A total of 47 microphotographs were taken from the 10 samples: 24 from the indoor air samples and 23 from the outdoor air. The latter showed the presence of only C > O > Cl, without the presence of elements typical of brake pads, unlike those detected in the remaining 24 microphotographs from the TMOW indoor air. As an example, Figure 2 shows the analyses obtained for three indoor air samples. For each sample, the photomicrograph, the spectral composition, and the weight percentages of the elements detected are shown.

In the chemical composition of the samples, the following elements were detected in order of molecular weight percentage: C > O > Si > Mg > Cl > Fe (Figure 2a), C > O > Rb > K > Mg (Figure 2b), C > Cl > O > Cr (Figure 2c), from compounds such as SiO₂, KCl, MgO and CaCO₃. Also, albite, undefined Rb, undefined Cr, Ba, and Mn were detected. In other samples also analyzed, C > O > Si > Al > K, C > O > Si > Mg > Cl > Fe, Cl > O > Al > Ca, C > O > Cl > Al > F, C > Cl > Al > Cu were detected.

The chemical composition of the 47 samples analyzed, expressed as the percentage by weight of each element detected, is shown graphically in Figure 3.

On the other hand, the average composition of all samples calculated from the values given in Figure 3 is shown in Figure 4.

In addition, the microphotographs made it possible to identify the size of the particles deposited on the filters. Thus, for instance, Figure 5 shows four microphotographs in which the sizes of the detected particles were determined.

The particle size ranged from 1.12 µm to 54.33 µm, with an arithmetic mean of 14.89 µm and a standard deviation (SD) of 13.36 µm; in ultrafine size, it ranged from 198 nm to 798 nm, with a SD of 169.19 nm.

Finally, Figure 6 shows the cumulative size distribution of all particles detected in the 47 samples in the TMOWs.

4. Discussion

The American Conference of Governmental Industrial Hygienists (ACGIH) has established a threshold limit value (TLV) of 2.5 mg/m³ for ultrafine titanium dioxide particles [28]. For other particles, they recommend a concentration not to exceed 3 mg/m³ for respirable particles and 10 mg/m³ for inhalable particles [28].

Therefore, taking the TLV of 2.5 mg/m³ as valid, the mean AOE measured exceeds this value by approximately 10 times. Furthermore, as can be seen in Table 1, all TMOWs exceeded the AOE this TLV.

Twenty percent of the samples taken from outdoor air exceeded the concentration of 2.5 mg/m³, due to the fact that these TMOWs were located in areas with high vehicular traffic. But in all cases, this outdoor concentration was much lower than that measured inside the TMOWs.

As for the chemical composition of the particles detected in the samples taken inside the TMOWs, as can be seen in Figure 4, the chemical elements detected by SEM from highest to lowest average percentage by weight were as follows: C > O > Cl > Si > Fe > Al > Ba > Cr > Mn > Mg > F > Ca > Rb > K > Cu > Na. It can be observed that C and O total more than 50%, probably due to the tire dust (CaCO₃ and SiO₂) present in the air of the workshop. On the other hand, the abundance of Cl (15.7%) could be due to Cl from the PVC filter used in the sampling.

The presence of Cr is shown in Figure 2c. The main chemical components of brake wear are Fe, Cu, Ba, and Pb. Organic carbon is also present in much higher concentrations than elemental carbon.

In terms of chemical composition, traces of CaCO₃, SiO₂, MgO, Al₂O₃, BaF₂, KCl, Fe, Cr, Mn, Rb, Cu, and MgF₂ were found, which are typical of components of refractory materials, fiberglass, asbestos substitutes such as wollastonite (CaSiO₃-Ca₃), thermoplastics, heat sealants, anti-corrosives, heat-resistant enamel, and thermal and electrical insulators, all related to brake pads and tires. Traces of Ca are most likely from wollastonite (silicate mineral used in the refractory industry), and Na from albite (silicate mineral used in ceramics and refractories).

The microphotographs shown in Figure 5 at a 10 µm scale show the different size ranges of particles from 1.12 µm (Figure 5b) to 54.33 µm (Figure 5d), which can be deposited in any part of the respiratory tract (inhalable, thoracic, and respirable), most likely causing respiratory pathologies in the different areas of the respiratory tract.

As shown in Figure 6, more than one-third of the particles detected are smaller than 5 µm and more than 50% are smaller than 10 µm, i.e., PM10. Given the sizes of the particles found, deposition in the respiratory tract is very likely to occur in the middle region, affecting the trachea, bronchi, and bronchioles. In addition, particles below 2.5 µm (PM2.5) were detected, which could affect the lower respiratory tract and, therefore, be a generator of pulmonary pathologies in TMOW workers, especially in the braking area. As for the AOE of the samples taken, it turned out to be higher than almost 10 times the TLV of ultrafine particles, considerably increasing the probability of causing sickness. A simple way to reduce the harmful effects of particulate matter on human health during testing would consist of providing workers with appropriate personal protective equipment (PPE), such as respirators similar to N95 (NIOSH-42CFR84, USA) or FFP2 (EN 149-2001, Europe) face masks, gloves, and protective clothing to limit exposure. However, during the visit to the different TMOWs, 90% of the workers did not use respiratory protection, which may represent a future occupational health problem for the workers.

5. Conclusions

The AOE is well above the theoretical TLV, which represents a very high risk to workers’ respiratory health. Regarding the chemical composition of the particles, it is important to highlight that Cr was detected as total Cr and that it was not defined as trivalent or hexavalent, which is considered to be highly dangerous.

From the particle size analysis, it can be deduced that approximately half of the particles are PM10 and the other half are above PM10. Therefore, half would be deposited in the upper respiratory tract. Particles between PM10 and PM2.5 would deposit in the middle respiratory tract and those below PM2.5 in the lower respiratory tract.

In view of these results, it is necessary to carry out exhaustive individual protection controls that protect workers from middle- and lower-tract respiratory problems. Despite the fact that most of TMOWs are open spaces, workers are exposed to fine and ultrafine particles. Almost none of the workers were observed to use appropriate PPE. In addition, it should be remembered that TMOWs also perform other tests that introduce other pollutants into the air, such as emission tests for combustion vehicles.

This research has allowed us to confirm the existence of fine and ultrafine particles in TMOW braking tests. Although the research was only carried out in TMOWs in Armenia (Colombia), we believe that these conclusions can be extended to any other TMOW as the brake test follows a standardized procedure.

This is a problem that will not go away with the advent of electric vehicles to replace internal combustion vehicles, as NEE particles are emitted by all wheeled vehicles.

Therefore, we recommended improvement actions based on epidemiological surveillance programs and the prevention of serious diseases of the middle and lower respiratory tract, generating a better quality of working life, as decreed by Colombian legislation through the Integrated Health Care Routes (better known as RIAS, its acronym in Spanish).