Sub-23 nm Particles Dominate Non-Volatile Particle Number Emissions of Road Traffic.

Ultrafine particles (<100 nm) in urban air are a serious health hazard not yet fully understood. Therefore, particle number concentration monitoring was recently included in the WHO air quality guidelines. At present, e.g., the EU regulates particle number only regarding the emissions of solid particles larger than 23 nm emitted by vehicles. The aim of this study was to examine the non-volatile fraction of sub-23 nm particles in a traffic-influenced urban environment. We measured the number concentration of particles larger than 1.4, 3, 10, and 23 nm in May 2018. Volatile compounds were thermally removed in the sampling line and the line losses were carefully determined. According to our results, the sub-23 nm particles dominated the non-volatile number concentrations. Additionally, based on the determined particle number emission factors, the traffic emissions of non-volatile sub-10 nm particles can be even 3 times higher than those of particles larger than 10 nm. Yet, only a fraction of urban sub-10 nm particles consisted of non-volatiles. Thus, while the results highlight the role of ultrafine particles in the traffic-influenced urban air, a careful consideration is needed in terms of future particle number standards to cover the varying factors affecting measured concentrations.

Snapshots of wintertime urban aerosol characteristics: Local sources emphasized in ultrafine particle number and lung deposited surface area.

Urban air fine particles are a major health-relating problem. However, it is not well understood how the health-relevant features of fine particles should be monitored. Limitations of PM2.5 (mass concentration of sub 2.5 µm particles), which is commonly used in the health effect estimations, have been recognized and, e.g., World Health Organization (WHO) has released good practice statements for particle number (PN) and black carbon (BC) concentrations (2021). In this study, a characterization of urban wintertime aerosol was done in three environments: a detached housing area with residential wood combustion, traffic-influenced streets in a city centre and near an airport. The particle characteristics varied significantly between the locations, resulting different average particle sizes causing lung deposited surface area (LDSA). Near the airport, departing planes had a major contribution on PN, and most particles were smaller than 10 nm, similarly as in the city centre. The high hourly mean PN (>20 000 1/cm3) stated in the WHO's good practices was clearly exceeded near the airport and in the city centre, even though traffic rates were reduced due to a SARS-CoV-2-related partial lockdown. In the residential area, wood combustion increased both BC and PM2.5, but also PN of sub 10 and 23 nm particles. The high concentrations of sub 10 nm particles in all the locations show the importance of the chosen lower size limit of PN measurement, e.g., WHO states that the lower limit should be 10 nm or smaller. Furthermore, due to ultrafine particle emissions, LDSA per unit PM2.5 was 1.4 and 2.4 times higher near the airport than in the city centre and the residential area, respectively, indicating that health effects of PM2.5 depend on urban environment as well as conditions, and emphasizing the importance of PN monitoring in terms of health effects related to local pollution sources.

Shipping Remains a Globally Significant Source of Anthropogenic PN Emissions Even after 2020 Sulfur Regulation.

Shipping is the main source of anthropogenic particle emissions in large areas of the globe, influencing climate, air quality, and human health in open seas and coast lines. Here, we determined, by laboratory and on-board measurements of ship engine exhaust, fuel-specific particle number (PN) emissions for different fuels and desulfurization applied in shipping. The emission factors were compared to ship exhaust plume observations and, furthermore, exploited in the assessment of global PN emissions from shipping, utilizing the STEAM ship emission model. The results indicate that most particles in the fresh ship engine exhaust are in ultrafine particle size range. Shipping PN emissions are localized, especially close to coastal lines, but significant emissions also exist on open seas and oceans. The global annual PN produced by marine shipping was 1.2 × 1028 (±0.34 × 1028) particles in 2016, thus being of the same magnitude with total anthropogenic PN emissions in continental areas. The reduction potential of PN from shipping strongly depends on the adopted technology mix, and except wide adoption of natural gas or scrubbers, no significant decrease in global PN is expected if heavy fuel oil is mainly replaced by low sulfur residual fuels. The results imply that shipping remains as a significant source of anthropogenic PN emissions that should be considered in future climate and health impact models.

Using an oxidation flow reactor to understand the effects of gasoline aromatics and ethanol levels on secondary aerosol formation.

Fuel type and composition affect tailpipe emissions and secondary aerosol production from mobile sources. This study assessed the influence of gasoline fuels with varying levels of aromatics and ethanol on the primary emissions and secondary aerosol formation from a flexible fuel vehicle equipped with a port fuel injection engine. The vehicle was exercised over the LA92 and US06 driving cycles using a chassis dynamometer. Secondary aerosol formation potential was measured using a fast oxidation flow reactor. Results showed that the high aromatics fuels led to higher gaseous regulated emissions, as well as particulate matter (PM), black carbon, and total and solid particle number. The high ethanol content fuel (E78) resulted in reductions for the gaseous regulated pollutants and particulate emissions, with some exceptions where elevated emissions were seen for this fuel compared to both E10 fuels, depending on the driving cycle. Secondary aerosol formation potential was dominated by the cold-start phase and increased for the high aromatics fuel. Secondary aerosol formation was seen in lower levels for E78 due to the lower formation of precursor emissions using this fuel. In addition, operating driving conditions and aftertreatment efficiency played a major role on secondary organic and inorganic aerosol formation, indicating that fuel properties, driving conditions, and exhaust aftertreatment should be considered when evaluating the emissions of secondary aerosol precursors from mobile sources.

Physical Characteristics of Particle Emissions from a Medium Speed Ship Engine Fueled with Natural Gas and Low-Sulfur Liquid Fuels.

Particle emissions from marine traffic affect significantly air quality in coastal areas and the climate. The particle emissions were studied from a 1.4 MW marine engine operating on low-sulfur fuels natural gas (NG; dual-fuel with diesel pilot), marine gas oil (MGO) and marine diesel oil (MDO). The emitted particles were characterized with respect to particle number (PN) emission factors, PN size distribution down to nanometer scale (1.2-414 nm), volatility, electric charge, morphology, and elemental composition. The size distribution of fresh exhaust particles was bimodal for all the fuels, the nucleation mode highly dominating the soot mode. Total PN emission factors were 2.7 × 1015-7.1 × 1015 #/kWh, the emission being the lowest with NG and the highest with MDO. Liquid fuel combustion generated 4-12 times higher soot mode particle emissions than the NG combustion, and the harbor-area-typical lower engine load (40%) caused higher total PN emissions than the higher load (85%). Nonvolatile particles consisted of nanosized fuel, and spherical lubricating oil core mode particles contained, e.g., calcium as well as agglomerated soot mode particles. Our results indicate the PN emissions from marine engines may remain relatively high regardless of fuel sulfur limits, mostly due to the nanosized particle emissions.

Toxicological evaluation of exhaust emissions from light-duty vehicles using different fuel alternatives in sub-freezing conditions.

BACKGROUND: Emissions from road traffic are under constant discussion since they pose a major threat to human health despite the increasingly strict emission targets and regulations. Although the new passenger car regulations have been very effective in reducing the particulate matter (PM) emissions, the aged car fleet in some EU countries remains a substantial source of PM emissions. Moreover, toxicity of PM emissions from multiple new types of bio-based fuels remain uncertain and different driving conditions such as the sub-zero running temperature has been shown to affect the emissions. Overall, the current literature and experimental knowledge on the toxicology of these PM emissions and conditions is scarce. METHODS: In the present study, we show that exhaust gas PM from newly regulated passenger cars fueled by different fuels at sub-zero temperatures, induce toxicological responses in vitro. We used exhaust gas volume-based PM doses to give us better insight on the real-life exposure and included one older diesel car to estimate the effect of the new emissions regulations. RESULTS: In cars compliant with the new regulations, gasoline (E10) displayed the highest PM concentrations and toxicological responses, while the higher ethanol blend (E85) resulted in slightly lower exhaust gas PM concentrations and notably lower toxicological responses in comparison. Engines powered by modern diesel and compressed natural gas (CNG) yielded the lowest PM concentrations and toxicological responses. CONCLUSIONS: The present study shows that toxicity of the exhaust gas PM varies depending on the fuels used. Additionally, concentration and toxicity of PM from an older diesel car were vastly higher, compared to contemporary vehicles, indicating the beneficial effects of the new emissions regulations.

Traffic is a major source of atmospheric nanocluster aerosol.

In densely populated areas, traffic is a significant source of atmospheric aerosol particles. Owing to their small size and complicated chemical and physical characteristics, atmospheric particles resulting from traffic emissions pose a significant risk to human health and also contribute to anthropogenic forcing of climate. Previous research has established that vehicles directly emit primary aerosol particles and also contribute to secondary aerosol particle formation by emitting aerosol precursors. Here, we extend the urban atmospheric aerosol characterization to cover nanocluster aerosol (NCA) particles and show that a major fraction of particles emitted by road transportation are in a previously unmeasured size range of 1.3-3.0 nm. For instance, in a semiurban roadside environment, the NCA represented 20-54% of the total particle concentration in ambient air. The observed NCA concentrations varied significantly depending on the traffic rate and wind direction. The emission factors of NCA for traffic were 2.4·1015 (kgfuel)-1 in a roadside environment, 2.6·1015 (kgfuel)-1 in a street canyon, and 2.9·1015 (kgfuel)-1 in an on-road study throughout Europe. Interestingly, these emissions were not associated with all vehicles. In engine laboratory experiments, the emission factor of exhaust NCA varied from a relatively low value of 1.6·1012 (kgfuel)-1 to a high value of 4.3·1015 (kgfuel)-1 These NCA emissions directly affect particle concentrations and human exposure to nanosized aerosol in urban areas, and potentially may act as nanosized condensation nuclei for the condensation of atmospheric low-volatile organic compounds.

Particulate Mass and Nonvolatile Particle Number Emissions from Marine Engines Using Low-Sulfur Fuels, Natural Gas, or Scrubbers.

In order to meet stringent fuel sulfur limits, ships are increasingly utilizing new fuels or, alternatively, scrubbers to reduce sulfur emissions from the combustion of sulfur-rich heavy fuel oil. The effects of these methods on particle emissions are important, because particle emissions from shipping traffic are known to have both climatic and health effects. In this study, the effects of lower sulfur level liquid fuels, natural gas (NG), and exhaust scrubbers on particulate mass (PM) and nonvolatile particle number (PN greater than 23 nm) emissions were studied by measurements in laboratory tests and in use. The fuel change to lower sulfur level fuels or to NG and the use of scrubbers significantly decreased the PM emissions. However, this was not directly linked with nonvolatile PN emission reduction, which should be taken into consideration when discussing the health effects of emitted particles. The lowest PM and PN emissions were measured when utilizing NG as fuel, indicating that the use of NG could be one way to comply with up-coming regulations for inland waterway vessels. Low PN levels were associated with low elemental carbon. However, a simultaneously observed methane slip should be taken into consideration when evaluating the climatic impacts of NG-fueled engines.

Strategies To Diminish the Emissions of Particles and Secondary Aerosol Formation from Diesel Engines.

Particle emissions and secondary aerosol formation from internal combustion engines deteriorate air quality and significantly affect human wellbeing and health. Both the direct particle emissions and the emissions of compounds contributing to secondary aerosol formation depend on choices made in selecting fuels, engine technologies, and exhaust aftertreatment (EAT). Here we study how catalytic EATs, particle filtration, and fuel choices affect these emissions concerning heavy-duty diesel engine. We observed that the most advanced EAT decreased the emissions of fresh exhaust particle mass as much as 98% (from 44.7 to 0.73 mg/kWh) and the formation of aged exhaust particle mass ∼100% (from 106.2 to ∼0 mg/kWh). The composition of emitted particles depended significantly on the EAT and oxidative aging. While black carbon typically dominated the composition of fresh exhaust particles, aged particles contained more sulfates and organics. The fuel choices had minor effects on the secondary aerosol formation, implicating that, in diesel engines, either the lubricant is a significant source of secondary aerosol precursors or the precursors are formed in the combustion process. Results indicate that the utilization of EAT in diesel engines would produce benefits with respect to exhaust burden on air quality, and thus their utilization should be promoted especially in geographical areas suffering from poor air quality.

Alzheimer's disease and alpha-synuclein pathology in the olfactory bulbs of infants, children, teens and adults ≤ 40 years in Metropolitan Mexico City. APOE4 carriers at higher risk of suicide accelerate their olfactory bulb pathology.

There is growing evidence that air pollution is a risk factor for a number of neurodegenerative diseases, most notably Alzheimer's (AD) and Parkinson's (PD). It is generally assumed that the pathology of these diseases arises only later in life and commonly begins within olfactory eloquent pathways prior to the onset of the classical clinical symptoms. The present study demonstrates that chronic exposure to high levels of air pollution results in AD- and PD-related pathology within the olfactory bulbs of children and relatively young adults ages 11 months to 40 years. The olfactory bulbs (OBs) of 179 residents of highly polluted Metropolitan Mexico City (MMC) were evaluated for AD- and alpha-synuclein-related pathology. Even in toddlers, hyperphosphorylated tau (hTau) and Lewy neurites (LN) were identified in the OBs. By the second decade, 84% of the bulbs exhibited hTau (48/57), 68% LNs and vascular amyloid (39/57) and 36% (21/57) diffuse amyloid plaques. OB active endothelial phagocytosis of red blood cell fragments containing combustion-derived nanoparticles (CDNPs) and the neurovascular unit damage were associated with myelinated and unmyelinated axonal damage. OB hTau neurites were associated mostly with pretangle stages 1a and 1b in subjects ≤ 20 years of age, strongly suggesting olfactory deficits could potentially be an early guide of AD pretangle subcortical and cortical hTau. APOE4 versus APOE3 carriers were 6-13 times more likely to exhibit OB vascular amyloid, neuronal amyloid accumulation, alpha-synuclein aggregates, hTau neurofibrillary tangles, and neurites. Remarkably, APOE4 carriers were 4.57 times more likely than non-carriers to die by suicide. The present findings, along with previous data that over a third of clinically healthy MMC teens and young adults exhibit low scores on an odor identification test, support the concept that olfactory testing may aid in identifying young people at high risk for neurodegenerative diseases. Moreover, results strongly support early neuroprotective interventions in fine particulate matter (PM2.5) and CDNP's exposed individuals ≤ 20 years of age, and the critical need for air pollution control.

Heavy Duty Diesel Exhaust Particles during Engine Motoring Formed by Lube Oil Consumption.

This study reports high numbers of exhaust emissions particles during engine motoring. Such particles were observed in the exhaust of two heavy duty vehicles with no diesel particle filter (DPF), driven on speed ramp tests and transient cycles. A significant fraction of these particles was nonvolatile in nature. The number-weighted size distribution peak was below 10 nm when a thermodenuder was used to remove semivolatile material, growing up to 40 nm after semivolatile species condensation. These particles were found to contribute to 9-13% of total particle number emitted over a complete driving cycle. Engine motoring particles originated from lube oil and evidence suggests that these are of heavy organic or organometallic material. Particles of similar characteristics have been observed in the core particle mode during normal fired engine operation. Their size and chemical character has implications primarily on the environmental toxicity of non-DPF diesel and, secondarily, on the performance of catalytic devices and DPFs. Lube oil formulation measures can be taken to reduce the emission of such particles.

Physical and Chemical Characterization of Real-World Particle Number and Mass Emissions from City Buses in Finland.

Exhaust emissions of 23 individual city buses at Euro III, Euro IV and EEV (Enhanced Environmentally Friendly Vehicle) emission levels were measured by the chasing method under real-world conditions at a depot area and on the normal route of bus line 24 in Helsinki. The buses represented different technologies from the viewpoint of engines, exhaust after-treatment systems (ATS) and fuels. Some of the EEV buses were fueled by diesel, diesel-electric, ethanol (RED95) and compressed natural gas (CNG). At the depot area the emission factors were in the range of 0.3-21 × 10(14) # (kg fuel)(-1), 6-40 g (kg fuel)(-1), 0.004-0.88 g (kg fuel)(-1), 0.004-0.56 g (kg fuel)(-1), 0.01-1.2 g (kg fuel)(-1), for particle number (EFN), nitrogen oxides (EFNOx), black carbon (EFBC), organics (EFOrg), and particle mass (EFPM1), respectively. The highest particulate emissions were observed from the Euro III and Euro IV buses and the lowest from the ethanol and CNG-fueled buses, which emitted BC only during acceleration. The organics emitted from the CNG-fueled buses were clearly less oxidized compared to the other bus types. The bus line experiments showed that lowest emissions were obtained from the ethanol-fueled buses whereas large variation existed between individual buses of the same type indicating that the operating conditions by drivers had large effect on the emissions.

Effects of fresh lubricant oils on particle emissions emitted by a modern gasoline direct injection passenger car.

Particle emissions from a modern turbocharged gasoline direct injection passenger car equipped with a three-way catalyst and an exhaust gas recirculation system were studied while the vehicle was running on low-sulfur gasoline and, consecutively, with five different lubrication oils. Exhaust particle number concentration, size distribution, and volatility were determined both at laboratory and on-road conditions. The results indicated that the choice of lubricant affected particle emissions both during the cold start and warm driving cycles. However, the contribution of engine oil depended on driving conditions being higher during acceleration and steady state driving than during deceleration. The highest emission factors were found with two oils that had the highest metal content. The results indicate that a 10% decrease in the Zn content of engine oils is linked with an 11-13% decrease to the nonvolatile particle number emissions in steady driving conditions and a 5% decrease over the New European Driving Cycle. The effect of lubricant on volatile particles was even higher, on the order of 20%.

Vehicle engines produce exhaust nanoparticles even when not fueled.

Vehicle engines produce submicrometer exhaust particles affecting air quality, especially in urban environments. In on-road exhaust studies with a heavy duty diesel vehicle and in laboratory studies with two gasoline-fueled passenger cars, we found that as much as 20-30% of the number of exhaust particles larger than 3 nm may be formed during engine braking conditions-that is, during decelerations and downhill driving while the engine is not fueled. Particles appeared at size ranges extending even below 7 nm and at high number concentrations. Their small size and nonvolatility, coupled with the observation that these particles contain lube-oil-derived metals zinc, phosphorus, and calcium, are suggestive of health risks at least similar to those of exhaust particles observed before. The particles' characteristics indicate that their emissions can be reduced using exhaust after-treatment devices, although these devices have not been mandated for all relevant vehicle types. Altogether, our findings enhance the understanding of the formation vehicle emissions and allow for improved protection of human health in proximity to traffic.

Sulfur driven nucleation mode formation in diesel exhaust under transient driving conditions.

Sulfur driven diesel exhaust nucleation particle formation processes were studied in an aerosol laboratory, on engine dynamometers, and on the road. All test engines were equipped with a combination of a diesel oxidation catalyst (DOC) and a partial diesel particulate filter (pDPF). At steady operating conditions, the formation of semivolatile nucleation particles directly depended on SO2 conversion in the catalyst. The nucleation particle emission was most significant after a rapid increase in engine load and exhaust gas temperature. Results indicate that the nucleation particle formation at transient driving conditions does not require compounds such as hydrocarbons or sulfated hydrocarbons, however, it cannot be explained only by the nucleation of sulfuric acid. A real-world exhaust study with a heavy duty diesel truck showed that the nucleation particle formation occurs even with ultralow sulfur diesel fuel, even at downhill driving conditions, and that nucleation particles can contribute 60% of total particle number emissions. In general, due to sulfur storage and release within the exhaust aftertreatment systems and transients in driving, emissions of nucleation particles can even be the dominant part of modern diesel vehicle exhaust particulate number emissions.

Optical and chemical characterization of aerosols emitted from coal, heavy and light fuel oil, and small-scale wood combustion.

Particle emissions affect radiative forcing in the atmosphere. Therefore, it is essential to know the physical and chemical characteristics of them. This work studied the chemical, physical, and optical characteristics of particle emissions from small-scale wood combustion, coal combustion of a heating and power plant, as well as heavy and light fuel oil combustion at a district heating station. Fine particle (PM1) emissions were the highest in wood combustion with a high fraction of absorbing material. The emissions were lowest from coal combustion mostly because of efficient cleaning techniques used at the power plant. The chemical composition of aerosols from coal and oil combustion included mostly ions and trace elements with a rather low fraction of absorbing material. The single scattering albedo and aerosol forcing efficiency showed that primary particles emitted from wood combustion and some cases of oil combustion would have a clear climate warming effect even over dark earth surfaces. Instead, coal combustion particle emissions had a cooling effect. Secondary processes in the atmosphere will further change the radiative properties of these emissions but are not considered in this study.

Exposure to source-specific air pollution in residential areas and its association with dementia incidence: a cohort study in Northern Sweden.

The aim of this study was to investigate the relationship between source-specific ambient particulate air pollution concentrations and the incidence of dementia. The study encompassed 70,057 participants from the Västerbotten intervention program cohort in Northern Sweden with a median age of 40 years at baseline. High-resolution dispersion models were employed to estimate source-specific particulate matter (PM) concentrations, such as PM10 and PM2.5 from traffic, exhaust, and biomass (mainly wood) burning, at the residential addresses of each participant. Cox regression models, adjusted for potential confounding factors, were used for the assessment. Over 884,847 person-years of follow-up, 409 incident dementia cases, identified through national registers, were observed. The study population's average exposure to annual mean total PM10 and PM2.5 lag 1-5 years was 9.50 µg/m3 and 5.61 µg/m3, respectively. Increased risks were identified for PM10-Traffic (35% [95% CI 0-82%]) and PM2.5-Exhaust (33% [95% CI - 2 to 79%]) in the second exposure tertile for lag 1-5 years, although no such risks were observed in the third tertile. Interestingly, a negative association was observed between PM2.5-Wood burning and the risk of dementia. In summary, this register-based study did not conclusively establish a strong association between air pollution exposure and the incidence of dementia. While some evidence indicated elevated risks for PM10-Traffic and PM2.5-Exhaust, and conversely, a negative association for PM2.5-Wood burning, no clear exposure-response relationships were evident.

Towards zero pollution vehicles by advanced fuels and exhaust aftertreatment technologies.

Vehicular emissions deteriorate air quality in urban areas notably. The aim of this study was to conduct an in-depth characterization of gaseous and particle emissions, and their potential to form secondary aerosol emissions, of the cars meeting the most recent emission Euro 6d standards, and to investigate the impact of fuel as well as engine and aftertreatment technologies on pollutants at warm and cold ambient temperatures. Studied vehicles were a diesel car with a diesel particulate filter (DPF), two gasoline cars (with and without a gasoline particulate filter (GPF)), and a car using compressed natural gas (CNG). The impact of fuel aromatic content was examined for the diesel car and the gasoline car without the GPF. The results showed that the utilization of exhaust particulate filter was important both in diesel and gasoline cars. The gasoline car without the GPF emitted relatively high concentrations of particles compared to the other technologies but the implementation of the GPF decreased particle emissions, and the potential to form secondary aerosols in atmospheric processes. The diesel car equipped with the DPF emitted low particle number concentrations except during the DPF regeneration events. Aromatic-free gasoline and diesel fuel efficiently reduced exhaust particles. Since the renewal of vehicle fleet is a relatively slow process, changing the fuel composition can be seen as a faster way to affect traffic emissions.

Characterizing winter-time brown carbon: Insights into chemical and light-absorption properties in residential and traffic environments.

Brown carbon (BrC) is an organic aerosol (OA) component that possesses light-absorbing properties in the UV-Vis spectrum, impacting climate. However, the current understanding of climate repercussions stemming from BrC emissions remains insufficient due to a lack of comprehensive knowledge regarding its chemical makeup, light-absorption, and the role of atmospheric aging in shaping BrC properties. This study investigates BrC in PM1 (particulate matter <1µm) during winter in Helsinki, Finland, in a street canyon and a residential area with wood combustion. The aim was to ascertain BrC sources, chemical composition, and contribution to UV-Vis light absorption. The study utilized a seven-wavelength aethalometer (AE33) to measure black carbon (BC) and BrC light absorptions, and a soot particle aerosol mass spectrometer (SP-AMS) to determine OA composition. An OA source apportionment using positive matrix factorization followed by a multiple regression analysis between BrC absorption and each factor was performed to determine the mass absorption coefficients of BrC (MACBrC) and light absorption contributions of distinct sources across 370-660 nm wavelengths. The BrC UV-Vis absorption relative to the one of BC was higher at 370 nm, with a median contribution of 20.1 % in the residential area and 18.2 % at the traffic site. Residential BrC absorption showed sporadic peaks, while street canyon absorption was lower but consistent. MACBrC was higher for biomass burning organic aerosol but still significant for long-range transported (LRT) and traffic-related aerosols. Hydrocarbon-like organic aerosol exhibited higher MACBrC at 470 nm than at 370 nm. Combined with particulate mass concentrations, biomass burning and LRT contributed the most to light absorption. Uncertainties regarding MACBrC were evaluated. The chemical composition analysis revealed stronger correlations between BrC absorption and SP-AMS-measured ions, especially in residential areas and for polycyclic aromatic hydrocarbons and oxidized aromatics. The study emphasizes the importance of anthropogenic sources in BrC light absorption.