'Crimes' of Black Carbon

I am a dark coat,
Keep the Earth hot.
I born from the flames and smoke,
Travelling with air and wind.
WHAT AM I?

fig.1 An introduction of black carbon

In the last post, I wrote about the Great Smog in London in 1952, which is mainly caused by soots, aka black carbon, that was formed by burning of coals. So... What is black carbon? Literally, it means something black, contains carbon. By definition from the US EPA, black carbon is ''Black carbon is the sooty black material emitted from gas and diesel engines, coal-fired power plants, and other sources that burn fossil fuel. It comprises a significant portion of particulate matter or PM, which is an air pollutant'. In the recent couple decades, black carbon has become a serious problem worldwide, especially in developing countries in Aisa. It is a major contributor to the fine particle (PM10 and PM2.5) in the atmosphere, which I usually check on my phone before going out. The data from those apps may not be very accurate, as it largely depends on the location of the monitor (e.g. more traffic more PM2.5), but at least it shows that black carbon and PM are now a large concern for the public. And this has everything to do with its threat to human health.

fig.2 An app showing real-time PM2.5 value.

Black Carbon's Impact on Human Health

Black carbon is a major contributor to the fine particle, aka PM2.5, which defined as particles less than 2.5 mm in aerodynamic diameter and can be easily inhaled into human lungs and has been associated with adverse health impacts.

According to an article by Pope and Dockery in 2006, numerous researchers have studied the impact of short-term exposure of fine particles, and come to a conclusion that, although the effect is relatively small, they observe adverse mortality associations with short-term elevations in ambient PM. Moreover, by 1997, Harvard Six Cities and ACS studies had reported evidence of mortality effects of chronic exposure to fine particulate air pollution. On the other hand, a study by World Health Organization shows that both short- and long-term effects estimates are generally much higher for black carbon compared to particle matters.

fig.3 Single-city, single-pollutant estimates for fine particle (PM10) and black carbon (BS) and all-cause mortality

A review by WHO of the results of all available toxicological studies suggested that black carbon may not act as a major directly toxic component of fine PM, but as a universal carrier of a wide variety of combustion-derived chemical constituents of different toxicity to sensitive targets in the human body such as the respiratory system, the body's major defence cells and probably the systemic blood circulation. Due to the porous structure of black carbon, it can transport other more harmful air pollutants, such as acidifying ions, trace metals, PAHs, and Dioxins and furans. This could cause deeper penetration of toxic pollutants into pulmonary system. However, there is a good fortune in the midst of bad. Since black carbon can absorb other harmful pollutants, by reducing black carbon, the spreading of other pollutants can be significantly controlled.

fig.4 Black carbon under microscope view

Black Carbon's Impact on the Environment

Black carbon is one of the most serious environmental problems nowadays, as It enhances climate change and can even affect rainfall patterns. Due to its dark colour, black carbon reduces albedo when it is carried by wind to polar areas and deposits on ices and snows. The effect is significant. According to the calculation by Hadley and Kirchestetter, with a small amount of black carbon (10 - 100 ppm), it can decrease the snow albedo by 1-5%. Lower albedo means more absorption of solar radiation, which leads to enhanced greenhouse effects and rising surface temperature. More ice melts at the higher temperature, and the loss of ice causes further temperature rise. This positive feedback, therefore, accelerates the global warming. Moreover, as black carbon heating up the atmosphere, it causes cloud droplets to evaporate. This process turns the cloud into a smoky haze that suppresses precipitation (Voiland, 2010).



All in all, black carbon causes severe damages to humans' cardiopulmonary and respiratory systems and have a significant impact on climate change and precipitation patterns. Although the emission of black carbon is mainly linked to industrial activities, as individuals, we could still make a contribution to the reduction of black carbon by less consumption of electricity, less driving, and promoting green energy such as solar and wind energy. In my following post, I will write about the present condition of black carbon in Asia (where the concentration is the highest) and what policies have been introduced to mitigate black carbon and fine particles.

London's Kiling Fog

To get a better idea of what is smog and the Great Smog incident, let's firstly watch a video by SciShow:

In previous posts, I mentioned the Meuse Valley air pollution incident that caused the death of over 60 people. This incident raised an alarm in the public and scientific community about how devastating air pollution can be. However, this did not bring the end of air pollution. On the contrary, it was only a beginning of series of tragedies caused by air pollution. In December 1952, a thick blanket of toxic smog shrouded London, killing an estimated 8,000 to 12,000 people (Klein, 2012).

Similar to the Meuse Valley incident, a high-pressure weather system with warm air above cold air prevented London's sulfurous coal smoke from rising. Moreover, there was, unfortunately, no wind to disperse the soot-laden smog. For five days, the Great Smog that was 30-mile-wide paralyzed London and crippled all ground transportation due to the poor visibility. 

fig.1 Image of a conductor in the Great Smog of London

Health Impact of the Great Smog

Same as most of the air pollution incidents, the elder, the young, and those with respiratory problems are the most affected by the Great Smog in 1952. Death from bronchitis and pneumonia increased more than sevenfold, and the death rate in London's east end increased by about nine times (Klein, 2012). According to a BBC report, 4,075 more people had died than would have been expected to under normal conditions. The death rate remained high above normal level until the summer of 1953. The majority in the scientific community now estimate the Great Smog claimed at least 8, 000 lives, even probably as many as 12,000.

fig.2 Deaths, sulphur dioxide concentration, and smoke in December 1952

The Great Smog's  impact on health is even long-term. according to an article by Bharadwa el al. (2016), exposure to the Great Smog in the first year of life increases the likelihood of childhood asthma by 19.87 percentage points. There is also suggestive evidence showing that early-life exposure led to a 9.53% higher likelihood of adult asthma, and exposure in utero led to a 7.91% higher likelihood of childhood asthma.


After the Great Smog

The incident in 1952 directly pushed British government to introduce the Clean Air Act in 1956. The act aimed to control domestic sources of smoke pollution by introducing smokeless zones, where smokeless fuels had to be burnt. Air quality in cities was dramatically improved through following methods:

• setting smoke control area to reduce domestic emissions;
• increase in electric and gas usage and the decline in solid fuel consumption;
• usage of cleaner coals with lower sulphur content;
• using tall chimney stacks on power stations;
• relocating power stations to rural areas;
• the decrease in heavy industry.

Next week, I'm going to post more about the second important pollutant (as sulphur dioxide was the major pollutant, and I've written about it in last two posts) in this incident, the black carbon particles. I will discuss how black carbon affects human health, and its contribution to modern environmental problems and climate change.

Success of Acid Rain Program in the US and WHY?

Regulations on sulphur dioxide emissions worldwide started as early as the mid-1900s. In today's post, I'm going to discuss the Acid Rain Program in the US, which started in 1970 and examine the 'secrets' behind its success.

In the US, The Clean Air Act achieved significant amendments since 1970 and established national standards for air pollutant and list of six criteria pollutants (including SO2) to be regulated by the Environmental Protection Agency (EPA). One of these early and most successful regulations on SO2 is the US's Acid Rain Program, which reduces SO2 emission through a market-based cap and trade system. The phase I of this program began as early as 1995 and had influences on 263 units (termed 'Table A' units) at 110 major coal-burning electric utility plants lied in 21 eastern and midwestern states. Another 182 units also joined Phase I of Acid Rain Program as substitutions or compensating units. In Phase I Table A units were allocated allowances equivalent to an emission rate of 2.5 pounds of SO2 per million Btu of heat input times the unit's heat rate in the 1985-1987 reference period (Chan et al. 2015). Phase II of the program began in 2000 and added more units to it. The units affected expended to over 2000 including smaller units fired by coal, oil, and gas. The program was quite effective, as it has achieved a 64% reduction compared to 1990 levels in 2009. The following graph demonstrates the decline of SO2 emission from 1985 to 2010 (Paramanand, 2012).

fig.1 Yearly Sulfur Dioxide and Nitrous Oxide Emission (in tons)

One of the reasons that the Acid Rain Program was so successful was the flexibility granted to the utilities to choose their method of compliance. This flexibility directly led to a high cost-effectiveness. For phase I, the estimated cost was $678 million to $1,511 million, while the cost has been now approximately $814 million. Actual compliance cost for phase II is now estimated to be $1.1 to $1.8 billion per year, much lower than the projected cost of $7.5 billion per year. Overall, fuel blending and fuel switching have been the most favored approaches to comply with the program. Utilities found it cost-effective to retrofit plants to utilize different types of coal and switch from high-sulphur coal to low-sulphur one or use a combination of both. The industry also benefited additional cost reduction due to the Stagger Act of 1980, which ended the monopoly Burlington Northen Railroad company had out of the Powder River Basin (the primary mine) (Paramanand, 2012 cited Ellerman, et al., 2000). With the increased competition in the railroad industry, the cost of transportation decreased. Moreover, the Acid Rain Program created incentives for research and development to reduce cost and improve efficiency, as utilities can sell unused permits (Paramanand, 2012 cited Popp, 2003). The program has caused the growth of secondary markets for emission permits. 

What's more, the market-based incentive programs to being efficient and cost-effective promoted the innovations in scrubber technology. According to Kumar and Managi (2010), technological progress for scrubber has increased 8% a year. The improvement in technology further lowered the cost to reduce SO2 emission and increased the efficiency.

The success of Acid Rain Program in the US was a combination of successful policy-making and development of the technologies and transportation. The market-based cap and trade system provides industries incentives to seek for the most efficient and cost-effective approach to sulphur reduction, while the progress in technology and lower transportation further lower the cost and increased efficiency. Moreover, the EPA's year allocated permits for auction and the Clean Air Market Database helped correct market failure, and lead to the efficient allocation of goods and services. The program is worth learning for many other nations for sulphur mitigation and can be used for reference to reduce other air pollutants.

Sulphur Dioxide and Its Impact on Human Health and The Environment

Sulphur dioxide is one of the greatest concern nowadays due to its toxicity at lower atmosphere and is used as the indicator for the larger group of gaseous sulphur oxides (SOx), since sulphur dioxide holds the highest concentration in the atmosphere compares with other sulphur oxides. As emissions of high concentrations of sulphur dioxide usually lead to the formation of other sulphur oxides, scientists found that control measures that reduce sulphur dioxide can generally be expected to decline people's exposures to all kinds of gaseous sulphur oxides. Nowadays, most of the sulphur dioxide comes from fossil fuel combustion at power plants and other industrial facilities, while we could also find sulphur particles during volcanic eruptions.

A Brief History of SO2

The oldest estimated sulphur dioxide emission data for most countries dates back to 1850, which was reconstructed based on fossil fuel production, imports, and industrial processing outputs. Industrialisation marked a significant transition point in the amount of sulphur dioxide emissions due to the large-scale burning of sulphur-containing fuels and industrial processing. Europe was the first one to show a rapid increase in sulphur pollution, followed by North America in the mid-19th century. As a result of increased energy demand of the industrialization, sulphur emission in Europe and North America did not stop rising until 1980 and 1970 respectively. In late 20th century and early 21st century, Europe, North America, and South America present a downward trend of sulphur emission. However, with the exception of Japan, industrialization in Asia, Latin America, and Africa began much later, and the sulphur emissions keep rising in those regions until present days.

fig.1 Regional emission of sulphur dioxide since 1850 to 2010

Health Impact

Some might be wondering that if sulphur dioxide also exists in the natural environment, for example, during a volcanic eruption, why should we concern about it? Isn't this nature? How could it affect our health and our environment? Well, unlike some other air pollutants, such as CO2, sulphur oxides merely stayed in the atmosphere, and only hold very low concentrations at the natural level. With industrial emission, exposures to this increased amount of sulphur dioxide in the atmosphere can harm the human respiratory system, and cause possible suffocation (like what happened in Meuse Valley).

 According to the Canadian Centre for Occupational Health and Safety (CCOHS), the most toxic route of exposure is inhalation, which 'can cause severe irritation of the nose and throat' at low concentration and 'cause life-threatening accumulation of fluid in the lungs (pulmonary edema)' at high concentration. It only requires a single exposure to a high concentration of sulphur dioxide to cause long-term conditions such as asthma. Sulphur dioxide is also capable of causing health effect through skin contact and eye contact, which could lead to irritation or burn of the skin and the eyes and might result in permanent scarring and blindness. Besides its impact on the respiratory system, according to European Environment Agency, sulphur dioxide could even affect the central nervous system and cause headaches, general discomfort, and anxiety. However, there isn't solid evidence of any correlation between cancer and sulphur pollution.

Fig.2 Illustration of health effect due to sulphur dioxide and other air pollutants

Environmental Impact

Apart from sulphur dioxide's health impact, it also causes serious problems to the environment we live in. One of the most concerned environmental impacts of sulphur dioxide is acid rain, which forms when sulphur dioxide is transported by wind and air current, and finally, react with water to produce sulphur acid. The concept of acid rain was firstly suggested by Robert Angus Smith in the 19th century. The sulphur acid can be deposited through wet deposition, such as rain, snow, fog, or hail; and dry deposition, when the acidic particles and gases accumulate in water bodies, vegetation, buildings, etc or when the particles react in the atmosphere and form larger particles. Those acid depositions can cause serious effects on the ecosystem and the environment.

fig.3 Pathway for acid rain in the environment

The ecological impacts of acid deposition are most common in aquatic environments, such as rivers, lakes, and oceans. When the acidic water flows through soils, it can leach aluminum from soil clay particles and then flow into water bodies. The more acidic the water is, the more aluminum it can release into the ecosystem.

Although some species of plants and animals are capable of tolerating acidic waters and a moderate amount of aluminum, others are acid-sensitive and will probably be harmed or even killed in low pH environment. The young of most species are usually more sensitive to environmental changes compare with the adults. When the pH level is as low as 5, most fish eggs would not be able to hatch, while some adult fish might die at lower pH levels, and some acidic lake does not even have fish. Even if some species of animal can tolerate the relatively high amount of acid and aluminum, the animal or plant it lives on may not. For instance, though frogs can survive a pH level around 4, the mayflies they feed on may would likely to be dead when the pH is under 5.5.

fig.4 This figure illustrates the pH level at which key organisms may be lost as their environment becomes more acidic. Not all fish, shellfish, or the insects that they eat can tolerate the same amount of acid.

Besides animals, when acidic water leaches aluminum from the soil, it also removes minerals and nutrients that plants required for growing. At high elevations, acidic fog and clouds can strip nutrients from trees' leaves, and decline the trees' ability to absorb sunlight. As a result, the plants would be too weak to survive the freezing temperatures.

Treatment and Regulations

In order to remove sulphur dioxide from waste gases after fossil fuel combustion, the power stations treat sulphur dioxide with powdered limestone to form calcium sulfate. The sulfate can be further used to make plasterboard for lining interior walls.

fig.5 Illustration of sulphur dioxide treatment in power stations

Sulphur can also be removed from the fuels at the oil refinery state. In 2008, the International Maritime Organization (IMO) has been aiming for a lower global limit for the sulphur content of ships' fuel oil in 2020, which will be 0.05% m/m (mass by mass).
While the global cap now is 3.50% m/m.

Conclusion

Sulphur dioxide is one of the most threatening air pollutants nowadays. It mostly comes from fossil fuel combustion for industrial purposes and vehicles. To humans, it can be deadly, as it is able to affect our respiratory system and even cause suffocation. To the environment and the ecosystem, the acid rain result from gaseous sulphur dioxide can lead to a decline in plant and animal population and biodiversity.

So shall we call sulphur dioxide 'guilty' for all those problems it caused? If we look at the source of the air pollution, it's obvious that at the end of the day, we humans are the one to blame for the air pollution and the further problems it leads to. It is our responsibility to control and minimize the negative impacts. Protecting the environment and reducing air pollution is not distant and is not the factories' problem along. Everyone can participate in protecting the environment and ourselves from air pollution by small things in our daily life, for example, turning off the lights when leaving the room, using public transport instead of driving, reducing consumption to decrease demand on fuels and energy, etc.