Carbon Air Pollution: Understanding Its Elemental Nature

Elemental carbon (EC) in the atmosphere originates from a variety of sources in many urban locations. It is produced by diesel engines and other combustion sources. EC is often studied in relation to air pollution and health, as it is important to understand its impact on air quality. EC is not usually found in pure particle form in the atmosphere, except near emission sources. In the atmosphere, it exists as black carbon, a mix of elemental and organic fractions. Black carbon is released during combustion, and elemental carbon is a significant component of it.

Elemental carbon (EC) is emitted from diesel engines and other combustion sources

Elemental carbon (EC) is a product of combustion released by diesel engines and other combustion sources. Diesel engines, like other internal combustion engines, convert the chemical energy contained in the fuel into mechanical power. During an ideal combustion process, diesel fuel—a mixture of hydrocarbons—would produce only carbon dioxide (CO2) and water vapour (H2O). However, in reality, the exhaust gases from diesel engines also include pollutants that can have adverse health and environmental effects. These pollutants arise from non-ideal processes during combustion, such as incomplete fuel combustion, reactions between mixture components under high temperature and pressure, and the combustion of engine lubricating oil, fuel additives, and non-hydrocarbon components of diesel fuel. Common pollutants include unburned hydrocarbons (HC), carbon monoxide (CO), nitrogen oxides (NOx), and particulate matter (PM).

EC is one of the components of particulate matter emitted by diesel engines and other combustion sources. It originates from a broad range of sources in many urban locations, and its concentration in the atmosphere is influenced by emissions from different regions. For example, a study in Amman, Jordan, found that sand and dust storms (SDS) led to higher EC concentrations than the annual means. Similarly, another study in Detroit, Michigan, investigated the apportionment of PM2.5 sources across sites and time periods.

The emission rates of EC from diesel engines depend on the mode of vehicle operation, such as highway, arterial, congested, and idling conditions. Various blends of diesel fuel with other substances, such as butanol, pentanol, and biodiesel, have been explored to reduce EC emissions. Modern diesel engines equipped with emission after-treatment devices, such as NOx reduction catalysts and particulate filters, have achieved "near-zero" levels of pollutants. However, the introduction of additives and catalysts into the fuel or lube oil can lead to new emissions, such as the release of highly toxic dioxins and furans.

Health and air quality studies use elemental carbon measurements to understand the impact of diesel engines and other combustion sources on the environment and human well-being. However, the different analytical techniques used to measure EC can lead to biases and inaccuracies in source contribution estimates. Therefore, it is crucial to integrate multiple analytical techniques and properly address all sources of EC in the atmosphere to accurately assess its impact.

EC concentrations are measured to understand the impact of diesel engines

Elemental carbon (EC) is produced in large quantities by diesel engines and only in trace amounts by petrol engines. As such, EC can be used as a marker of exposure to diesel engine exhaust emissions (DEEEs) in the workplace, especially in places where diesel engines are the only likely source of EC, such as coal mines.

Health and air quality studies measure EC concentrations to better understand the impact of diesel engines and other combustion sources on the environment and human health. These studies aim to identify the relative source contributions to EC concentrations in the atmosphere. However, different analytical techniques used to measure EC can lead to inconsistencies and biases in the results. Therefore, it is crucial to integrate multiple analytical techniques and properly address all sources of EC in the atmosphere to obtain accurate estimates.

One study reviewed the air quality data in harbour areas worldwide, where emissions from marine diesel engines affect the health of nearby residents. The research proposed a methodology using an exhaust gas analyser along with the recording of load indicator, engine speed, inclinometer, and GPS data to measure emissions from marine diesel engines without directly measuring fuel consumption and airflow.

Another study focused on the urban background in an Eastern Mediterranean city, Amman, Jordan. It found that during sand and dust storm (SDS) episodes, EC concentrations were higher than the annual means, indicating the introduction of particulate phase pollutants to the region. This study suggested that a large fraction of carbonaceous aerosol mass likely originates from anthropogenic activities.

To address the impact of diesel engines on the environment and human health, governments have implemented initiatives such as the Diesel Emissions Reduction Act (DERA) in the US. This program provides grants and rebates to eligible entities for projects that reduce emissions from existing diesel engines, contributing to improved fuel economy and idle reduction strategies.

EC is not a unique tracer for diesel exhaust

Elemental carbon (EC) is a significant component of air pollution in urban areas. It is produced by a broad range of sources, including diesel engines and other combustion sources. While EC is often used as a tracer for diesel exhaust in health and air quality studies, it is important to note that EC is not a unique tracer for diesel exhaust.

EC is one of the major components of diesel particulate matter (DPM), which is a mixture of gases and particles produced during the combustion of diesel fuel. DPM consists of solid EC cores with organic carbon (OC) compounds adhered to their surfaces. The OC compounds can include polyaromatic hydrocarbons (PAH), some of which are known to cause cancer in animal tests. Due to the health risks associated with exposure to diesel exhaust, it is crucial to accurately assess its impact on human health and the environment.

However, the use of EC as a tracer for diesel exhaust has limitations. Firstly, EC originates from various sources, and diesel engines are not the only contributors to EC concentrations in the atmosphere. Other combustion sources, such as gasoline engines and industrial processes, also release EC into the air. Therefore, attributing EC concentrations solely to diesel exhaust can lead to inaccuracies and biases in source attribution studies.

Additionally, the measurement techniques used to quantify EC can vary, and different analytical techniques may not agree with each other for many particulate matter samples. This inconsistency in measurement methods can further bias estimates of source contributions to atmospheric particulate matter. To improve the accuracy of using EC as a tracer, it is essential to address all sources of EC in the atmosphere and employ consistent and comprehensive measurement techniques.

Furthermore, the emission profile of diesel exhaust can vary depending on vehicle operating conditions and fleet characteristics. The age and maintenance of vehicles, as well as driving cycles, can influence the composition of diesel exhaust. Therefore, the use of EC as a tracer must consider the specific context and characteristics of the diesel sources being studied.

In summary, while EC is often used as a tracer for diesel exhaust, it is not unique to diesel emissions. To enhance the accuracy of source attribution studies and air pollution assessments, it is crucial to acknowledge the diverse sources of EC and employ consistent and comprehensive measurement techniques. By addressing these complexities, we can better understand the impact of diesel exhaust on human health and the environment and develop more effective strategies to mitigate its adverse effects.

EC concentrations are influenced by emissions from Africa, Asia, and Europe

Elemental carbon (EC) in atmospheric particulate matter originates from a wide range of sources in many urban locations. EC concentrations are influenced by emissions from Africa, Asia, and Europe. The Mediterranean region is a critical area for air pollution as it sits at the crossroads of these three continents.

A study in Amman, Jordan, found that sand and dust storms (SDS) introduced particulate phase pollutants, leading to higher EC concentrations. The annual mean EC concentration in PM2.5 samples was 1.7 ± 1.1 µg m–3, while during SDS episodes, the mean concentration increased to 2.5 ± 1.2 µg m–3. These findings highlight the impact of natural events on EC levels.

When considering global emissions, Asia, particularly China, stands out as the largest emitter, contributing more than a quarter of global emissions. The increase in emissions from China and other emerging economies has significantly contributed to the rise in global greenhouse gas concentrations. North America, dominated by the USA, is the second-largest emitter, followed by Europe, which historically emitted a large proportion of CO2, especially the United Kingdom until the late 19th century.

While Africa and South America are smaller emitters, accounting for 3-4% of global emissions each, their contributions are similar to those of international aviation and shipping combined. It is worth noting that the average emissions per person vary significantly, with some of the poorest countries in Sub-Saharan Africa having much lower emissions than developed nations like the USA, Australia, and Canada.

To fully understand the impact of emissions on EC concentrations, it is crucial to employ consistent measurement techniques and consider all sources, including diesel engines and other combustion sources.

EC concentrations are higher during sand and dust storms

Elemental carbon (EC) in atmospheric particulate matter originates from a wide range of sources in many urban locations. As health and air quality studies increasingly use elemental carbon measurements to understand the impact of diesel engines and other combustion sources, it is vital to comprehend the relative source contributions to EC concentrations in the atmosphere.

Sand and dust storms (SDS) are common meteorological hazards in arid and semi-arid regions, generating large amounts of airborne mineral dust particles. These storms present a widespread threat to health and sustainable development, impacting not only human health and air quality but also agriculture, the environment, industry, transport, and water quality. SDS episodes contribute directly to air pollution by increasing particulate matter concentrations.

During an eleven-month study in Amman, Jordan, it was found that EC concentrations were higher during SDS episodes than the annual means. The mean EC concentration during these periods was about 2.5 ± 1.2 µg m–3, compared to an annual mean of 1.7 ± 1.1 µg m–3. This indicates that SDS episodes introduce particulate phase pollutants other than coarse-mode dust particles to the region.

Furthermore, studies have shown that a large fraction of carbonaceous aerosol mass likely originates from anthropogenic activities rather than natural sources. For example, an estimated 25% of dust emissions result from human activities such as deforestation, land degradation, unsustainable land management, climate change, and water mismanagement. Climate change contributes to desertification, increasing the frequency and spread of SDS.

Understanding the relationship between EC concentrations and SDS is crucial for regulating involved activities and implementing effective public health responses.

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