Weekly ponderings: Last “official” post!

That marks the end of my blog posts to be assessed! (The blog assignment is due to run until 9 April). So I won’t post anything in these couple of weeks while exams are coming (in fact I have one next Monday). I’ve popped by some other people’s blog and saw some that made such similar announcement, so I thought I should do it too to mark a closing. I can’t guarantee that I will (or can) keep the blog running after the semester officially ends, because by then there is nothing to ground me to blogging but my own desire and will and motivation. I wouldn’t count on it, but we will have to wait for the future to prove that.

It has been wonderful keeping up this blog for the past few months! I will admit, it was difficult at times to write a blog post coherently because I couldn’t find information related to the themes I want to talk about (especially the more random ones). And it was also stressful at times, particularly at the start of the assignment as I wasn’t sure how best to write and present what I want to say. I guess as I move on and do more blogging I wanted to say everything in my own voice, and to not feel restricted by the more “popular” or “important” topics, whatever they mean. I hope you have enjoyed reading the blog as much as I have putting them together! (:

*Note to Prof Taylor, the first post of my blog can be found here, if you like to assess the blog chronologically from the beginning.

How much greener are hybrid cars?

In continuing the topic of vehicle air pollution (besides the small tangent on tropospheric vs stratospheric ozone), I would like to talk about the hybrid cars.

Hybrid cars are fuel efficient cars, with an electric motor and gasoline powered motor. You might have heard that hybrid cars are green, and more environmentally friendlier than traditional gasoline powered cars. In fact, I remember all those many years ago when I was still in Secondary 2, it was a topic for a project on green technology. If these cars are imaged as so, it must be true right?

In 2011, the Union of Concerned Scientists (UCS) developed a hybrid scorecard rating the reduction of air pollution of each hybrid.

hybrid scorecard non luxury

hybrid scorecard luxury
Tables showing the score of each hybrid vehicle in reducing air pollution. Scores are computed based on comparison with their conventional non-hybrid counterpart. Combined mpg (miles per gallon) represent the increased fuel efficiency, GHG (greenhouse gas) score is the relative ranking based on percentage of GHG reduction, Air pollution score is the relative ranking based on absolute air pollutants emitted and Environmental improvement score is the average of the two scores. Source. 

So what are some conclusions from the scorecard analysis of hybrid cars?

  • Hybrid cars are not necessarily the same as “green” cars! Some hybrids are greener than others, and we need to be aware of that before we automatically attribute hybrid cars as green.
  • A reduction in GHG emissions does not mean a reduction in air pollutants or vice versa. In some cases, the hybrid cars scored high on the air pollution score but relatively lower on the GHG score.

That being said, this article was written in 2011, and we are already in 2015. A optimistic sign since then is the continual decrease in the amount of pollutants emitted by cars (both GHG and other air pollutants).

The most up to date analysis by the UCS was published in 2014 and can be accessed via the picture link below. It should be noted however, that the methods of ranking is different from the scorecard ranking mentioned in this post.

If you are interested in the economic aspect of the hybrid car from the consumer perspective, you may read this article linked here, which describes the cost of owning a hybrid. It is an outdated article (published in 2006) but cost is still an issue that might hinder consumers from purchasing hybrids.



Dunn, P. (2006). Hybrid Cars — Pros and Cons. [Online]. Available from: http://phys.org/news10031.html

Holzman, D. C. (2011). Scorecard Rates Emission Reductions of Hybrid Vehicles. Environmental Heath Perspectives. [Online]. Available from: http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3230416/?tool=pmcentrez

In the Nation. (2014). Alternative Fuel Vehicles: What are the Pros and Cons? [Online]. Available from: http://www.inthenation.com/pros-cons-of-different-vehicle-types/.

Tuttle, B. (2014). Why Hybrid and Electric Cars Have Lost Their Spark. Time. Available from: http://time.com/money/3269068/hybrid-electric-cars-sales-nissan-leaf-tesla/.

Union of Concerned Scientists. (2014). Automaker Rankings 2014: The Environmental Performance of Car Companies. [Online]. Available from: http://www.ucsusa.org/clean_vehicles/what_you_can_do/automaker-rankings-2014.html#.VSYjF_mUdSE

The multi-facet nature of ozone

As explained in my last blog post, this post is to clarify any assumptions, misconceptions and confusions you may have about ozone. In a previous post about vehicle air pollution, I mentioned that tropospheric ozone is a form of pollutant, which may get you confused, because you might have heard that ozone is beneficial to us as they block harmful cancer-causing UV rays from the sun.

The fact is, both of these are true. They are the same chemical compound, with three oxygen atoms joined together to form O3. But when they occur at different altitude in the atmosphere, they have different effects on our health.

First of all, let’s look at the different layers of our atmosphere:

Structure of our atmosphere. Image source.
Commonly known heights in relation to the atmospheric layers. Image source.

Our atmosphere can be broadly divided into four sections as show in the diagram above, and of interest to our topic today is the two lowest layers, the troposphere and stratosphere. Ozone, when found in either of these layers will have a different effect on us.


1. Stratospheric Ozone

This category involves ozone that are found in our stratosphere, more commonly known as the ozone layer. At this altitude, ozone is good for us, because it absorbs harmful UV ray from the sun and hence they do not reach the ground. These UV rays can cause skin cancer and without the ozone layer, many people will get skin cancer just by going out into the sun. That being said, it is still important to protect yourself from harmful UV rays by not staying in the sun for prolonged periods of time even with sunblock applied. Not all UV rays can be absorbed by stratospheric ozone and hence some amounts of UV can still reach the ground and harm us.


2. Tropospheric Ozone

This category involves ozone that are found in our troposphere, which is the layer of atmosphere that we live and breathe in. At this altitude, ozone does not form a protection ozone layer but instead, they are compounds that harm our living tissues. Such ozone have been linked to tissue decay and cell damage by oxidation. People who exercise outdoors or have respiratory problems are particularly vulnerable to tropospheric ozone.

Tropospheric ozone can be found naturally, from hydrocarbons released by plants and soils, as well as stratospheric ozone that occasionally migrated to this lower altitude. At these small natural concentration, ozone is not harmful to us. But as mentioned in a previous post, vehicles emit pollutants that react with sunlight to form tropospheric ozone, a main component of photochemical smog. Photochemical smog is most commonly seen as a brown haze that blankets some cities such as Los Angeles and Sydney. An overview to photochemical smog, its components, health impacts and chemistry of smog formation can be viewed from this document by the Australian Environment Protection Authority.

Los Angeles blanketed by photochemical smog. Image source.

Other common terms for tropospheric ozone includes ground level ozone and “bad” ozone. This website, which is also stated in my reference list below, also offers a look into transporting these harmful tropospheric ozone into the stratosphere, which is an interesting concept of transferring ozone from a harmful location to a more beneficial one.



Environment Protection Authority, Australia. (2004). Photochemical smog – what it means for us. [Online]. Retrieved from: http://www.epa.sa.gov.au/xstd_files/Air/Information%20sheet/info_photosmog.pdf.

Herman & Newman. (2015). Ozone and UV: Where Are We Now? [Online]. Retrieved 6 April 2015 from: http://www.skincancer.org/prevention/uva-and-uvb/ozone-and-uv-where-are-we-now

NBC News. (2004). Most Americans live in bad smog areas. [Online]. Retrieved from: http://www.nbcnews.com/id/4862359/ns/us_news-environment/t/most-americans-live-bad-smog-areas/#.VSFgbfmUdjc.

University Corporation for Atmosphere Research. (2001). Tropospheric Ozone. the Polluter. [Online]. Retrieved from: https://www.ucar.edu/learn/1_7_1.htm.



Weekly ponderings: Spotting assumptions

I mentioned in my previous Weekly ponderings that a goal of this blog is to tackle assumptions and misconceptions and I “find” assumptions through different processes. Some of these assumptions are my own, and I discovered them as I do research for this blog, when I find things that contradict what I thought I believed. Other assumptions and particularly misconceptions are not my own but I thought that they could be some common assumptions or misconceptions that other people might have. As the theme of this blog and the content are very closely related to what I learn as part of my study discipline, some of the things that I know as a basic facts are not what other people know as a basic fact. As a result of that, I try to be really careful when I write my blog posts, trying to leave no stones unturned. This is one reason why I have my scientific explanation posts and glossary for some blog posts that I thought were too technical, as well as “follow up” blog posts explaining certain things, which is why I will link older blog posts to newer ones.

I write this now because I spotted an assumption/misconception in my previous blog post. In the post I mentioned tropospheric ozone and I thought people might be confused as to why they is a pollutant when it protects us from harmful UV rays. I had initially wanted to explain that here but most of the post is not relevant to the topic so that will be placed in the next blog post instead.

The end of the assignment is coming soon! Seems like I won’t finish posting all my planned posts that I had because I let spontaneous wonderings and thoughts dictate the main flow of the blog. But I like that because I learnt about the topics in the process as well.

Vehicle air pollution

Pollutants from vehicles are a key source of air pollution in many cities. In the US, they are the largest single source of pollutants and there are many studies to show the links between vehicle air pollution and health.

Here are some of the major hazardous components of vehicle exhaust and their health effects:

  • Hydrocarbons: These are organic compounds that are made up of carbon and hydrogen atoms. They contribute to smog by reacting with nitrogen oxides in the presence of sunlight to give rise to tropospheric ozone. They also have health effects such as reducing our lung capacity and irritating our respiratory system, causing coughing and choking.
  • Nitrogen oxides, NOx: NOx originates from vehicle exhaust, and can cause lung irritation. They also weaken our body’s defences against respiratory infections such as pneumonia and influenza. They also form other pollutants such as tropospheric ozone and PM.
  • Carbon monoxide, CO: Carbon monoxide is formed from the incomplete combustion of fuel in vehicles. When inhaled, CO competes with oxygen in our blood stream, and as a result they are cause a lack of oxygen in our body. In extreme cases, they may cause asphyxia (severe deficient of oxygen supply) and death and is the reason why you should never stay in a stationary car with the engines turned on and windows completely closed. Some groups are more vulnerable to the effects of CO, such as small children and people with chronic illness.
  • Hazardous air pollutants, HAP: Vehicle exhaust are the main source of HAP. The US Environment Protection Agency (EPA) has categorised them as a priority pollutant which means that they are highly toxic with serious health effects. They include compounds such as polycyclic aromatic hydrocarbons (PAH). They can be found naturally, but the majority of them are anthropogenic. These compounds are some of the most carcinogenic pollutants, and they have a tendency to bind with fine PM. In particular, they stay stored within our fat tissues once they enter our bodies, which can cause DNA mutation and cancer.
  • Greenhouse gases: Greenhouse gases are the gases responsible for global warming, which is then an effect of air pollution. The most common form is carbon dioxide which is formed from the combustion of fuel.

You may find from this short list of pollutants above, that many of these compounds or group of compounds are unfamiliar to you. For those that are familiar, you may also notice that they are the same pollutants that are being measured in our PSI. In actual fact, composition of pollutants are highly varied and the category of hazardous air pollutants itself consists of hundreds of different chemical composition. But the one common thing they are share is that they have serious health impacts particularly linked to respiratory diseases and cancer.



Union of Concerned Scientists. (2014). Cars, Trucks and Air Pollution. [Online]. Retrieved 30 March 2015 from: http://www.ucsusa.org/clean_vehicles/why-clean-cars/air-pollution-and-health/cars-trucks-air-pollution.html#.VR7Kw_mUdEq.

Union of Concerned Scientists. (n.d.). Diesel Engines and Public Health. [Online]. Retrieved 5 April 2015 from: http://www.ucsusa.org/clean_vehicles/why-clean-cars/air-pollution-and-health/trucks-buses-and-other-commercial-vehicles/diesel-engines-and-public.html#.VSFKiPmUdjd.

United States Environmental Protection Agency (2008). Polycyclic Aromatic Hydrocarbons (PAHs). [Online]. Retrieved from: http://www.epa.gov/osw/hazard/wastemin/minimize/factshts/pahs.pdf

Weekly ponderings: Achievement unlocked

The blog has been up and running for about 2 months now and I feel a little proud of what I have done so far. Then again, I’m a person who always celebrated small achievements, so it may not seem like a huge thing for other people. But here’s why I am proud of myself:

  • I don’t have a large number of posts, but I take pride in what I write, because I spend a lot of time looking up on each topic and to relay information in a succinct and yet it is not dumbed down.
  • I got a couple of friends to read through my blog posts earlier on in the assignment and received feedback that they really learnt some things about air pollution, particularly my posts that addresses common misconceptions and assumptions (which incidentally, were my personal misconceptions and assumptions too). So I feel like through my blog, I can achieve this small goal which I keep at the back of my head as I write my blog posts.
  • I like how neat I have managed the blog interface, particularly the catalogue of post I have done at the sidebar. Because what I look for in a good blog is the ease of retrieving things you have previous read or if you want to read more of similar topics.
  • I am most proud of the scientific explanations I have written for some specific topics, because I believe that some basic science is important to fully understand pollution. Distilling scientific explanations in layman terms was not easy, and I think this was what people meant when they said you have not fully understood something you have learnt until you can teach it to someone else.

It sounds like I’m boasting of what I’ve done but as I previously mentioned, I was never diligent at keeping a blog so all these are small achievements for myself. The thought of it being an assignment had kept me going and not completely stop blogging but that doesn’t mean to say that I post what I post for the sake of posting. That was never the case, because while reluctant at times, I take every blog post as a learning experience (in the broadest sense of the word, including academic learning, blogging learning and writing learning). And hence, I feel like it’s a great big achievement unlocked through writing this blog.

Air pollution in Singapore

Singapore is a clean and green city. Except for those episodes of transboundary haze issues, our air looks really clean. Look up and we see blue skies and white puffy clouds (or dark ominous rain clouds if it is about to rain) and even the air doesn’t smell of anything. So you think that Singapore is not plagued by air pollution? Think again.

Here are some statistics about air pollution in Singapore that would leave you wondering about air pollution in Singapore: between 1990 and 2008, Singapore reduced its COemissions by 31% BUT we still have a high per-capita COemission compared to most developed countries

Per-capita greenhouse gas emissions for selected cities around the world. CO2e includes not carbon dioxide but also nitrous oxide, methand, perflurocarbons (PFCs), hydroflurocarbons (HFCs) and sulfur hexafluroride (SF6). Numbers inside bars corresponds to baseline years. Source: Velasco and Roth (2012).

Surprising? I’m not sure about you, but I sure was. I guess both you and I are guilty of emitting this per capita amount each year. But no, another common misconception I believe, because that was what I thought so too.

I had a heated discussion with another friend over the use of per capita emission as comparison among different countries. I was arguing for using the per capita emission as a useful yardstick for measuring, because it was made to be comparable – keeping to the same time frame, as well as taken into account the population of the country. The comparibility of the index means we can tell at a glance which countries have more serious emission issue. He was arguing that we need something more than per capita because it doesn’t tell us much about why different places emit different amount of COand the over-simplistic look into emission because different places have different sources of pollution and some sources necessarily have high amount of emissions.

It got me thinking for a few weeks.  So here I am, questioning my own assumptions and hopefully, yours as well. We look back at my friend’s argument, and he said that different places have different sources of pollution. So here are the major sources of pollutant gases in Singapore (in no particular order):

  • Power plant (burning of natural gas and to a lesser extent, oil)
  • World’s third largest petroleum refining centre
  • Industrial sectors (chemical, electronic, metallurgic)
  • Waste incinerator
  • One of the busiest shipping ports in the world
  • Largest airport in the region
  • Vehicles
  • Private apartments

Within this short list, you find that a majority of these sources come from the industrial sector and not from personal emission. These industries necessarily emit larger amount of emission but they were calculated as part of per capita emission. In addition, the majority of these emissions were not for our personal benefit, for instance, petroleum refineries supplies many other countries, as does our ports and airports. To attribute all these emission to the whole of Singapore’s pollution and to “blame” Singapore for high amount of emissions would seem unfair in this instance. Afterall, we can’t possibly shut down all these industries forming our economic backbone to dramatically reduce pollution can we?

On the other hand, what Singapore can do is to minimise pollution, particularly in these pollutive sectors through more stringent policies and research into methods of reducing pollution. We seemed to have came a full round here, on the responsibility of the government to reduce emission of the entire country. My main point is this: per capita emissions doesn’t necessarily reflect the emissions of the population; some industries are more pollutive than others but high levels of emissions reflects government’s attitude and action in combating greenhouse gas emissions.



Velasco and Roth (2012). Review of Singapore’s air quality and greenhouse gas emissions: Current situation and opportunities. In: Journal of the Air & Waste Management Association. [Online]. Available from: http://www.tandfonline.com/doi/abs/10.1080/10962247.2012.666513#.VRgg0vmUdjc


Tom Lehrer’s Pollution

For a lighter note on the issue of pollution, I found this song by Tom Lehrer that was called, well “Pollution”:

Tom Lehrer is a American who writes satirical songs such as this. He composed satirical songs in the 1950s and 60s. I was introduced to him by a friend who like to listen to his satirical songs and this particular one caught my attention. The lyrics can be found here and the YouTube description of the video is as follows:

“A film of “Pollution”, featuring a cartoon of a bird playing a piano at a dump, combined with real scenes of industrial excess from across America, was made in 1966 & 1967 by Astrafilms for the U.S. Communicable Disease Center (not the Environmental Protection Agency as previously reported). The first cut in 1966 featured the live recording of “Pollution” from the LP, but this version of the film was not used. It was then redone in 1967, using more drastic scenes to really drive home the message. Tom and the producers agreed that it would be better to use a studio recording of the song without the audience, so he re-recorded it for the second version. It was then distributed by the National Medical Audio-Visual Center.

You might know Tom Lehrer as the singer of the element song, There are many other songs that he has written as well (my personal favourite is this).

No more blue skies?

I’m fascinated with the sky. I like to look up and see the blue of the sky, the shape of the clouds, and especially the stars that dot the night sky. I mentioned in my previous post, that clouds will be increasingly common with more aerosols and polluted skies. For me, that means I cannot see stars as often if that was true. But I would still have my blue sky, and my white puffy clouds. But what if that doesn’t happen too?

I chanced upon one Facebook post posted by my friend who is currently studying in Beijing. She started off by saying how she has taken clean air for granted, and how when she first arrived in Beijing people had jokingly asked her how many times can she see buildings clearly or whether she wore masks 24/7, and that she brushed off all these questions without much thought. I reckon if I were in her shoes, or if I was from Beijing, I would have done the same. In the post, she mentioned a documentary by Chai Jing that documents the air pollution situation in China. The video has since been banned by the Chinese government, but the video remains view-able on YouTube:

The language is in Chinese, but the video has excellent English subtitles. It is a rather impactful video, and it places a very personal face to the air pollution situation in China as well as a big chunk of food for thought. I started off talking about blue skies, clouds and stars, and it pains me to know that children in some parts of China are denied this enjoyment of the natural environment. A summary of the video can be found here if you prefer to read than to watch the entire length of the video.

Aerosols and cloud formation

On my last post on Chinese New Year, I wrote about the implications of the cultural association of fireworks and firecrackers on air pollution. That very night, before the sun has set I walked out of my grandfather’s house and looked up in the sky. The skies was perfectly clear, and even though the sun has not completely set and the sky was still pretty much a bright blue, I could spot starts and constellations, particularly the constellation of Orion. A few hours later, and after a few series of fireworks and firecrackers all around our house have been heard, I went out to look at the stars again. The difference was dramatic. In place of the clear skies and bright stars, all I could see were sporadic clusters of clouds and not a single star could be seen even though the sky was completely dark by then. I had a hunch that this was probably to do with the pollution from all the firecrackers and fireworks and so I wanted to find out if my hunch was correct.

I found this journal article which talks about aerosol forcing and cloud formation: From aerosol-limited to invigoration of warm convective clouds (the link leads to the article abstract). The main points of the article are as follow:

  • Aerosols serve as cloud condensation nuclei, which are surfaces on which water vapour condenses on in the atmosphere to form clouds.
  • In pristine environment i.e. largely pollution free, the lack of aerosols from pollution makes the environment aerosol limited. This means that there is a limitation on the available surface area on which water vapour can condense and thus, cloud mass are small.
  • In more polluted environment, the abundance of aerosols increases available surface area for water vapour to condense and create larger cloud mass. A positive feedback occurs, whereby larger cloud mass attracts more water vapour to condense, causing even larger cloud mass. This process is known as cloud invigoration.
  • Results from the research suggest that clouds forming in a pristine environment may be the most sensitive to changes in aerosol loading. This means a relative small input of aerosols into pristine environment would result in a greater cloud invigoration than the same input of aerosols in a more polluted environment.
  • The paper also highlights the dual effects of increased clouds formation: thicker and larger clouds reflect more shortwave radiation from the sun back to space thus cooling the atmosphere, but also have lower temperatures at cloud tops which emit less longwave radiation to space thus warming the atmophere. The overall effect is a net cooling effect. For more explanation on radiative properties and definitions, refer to this page.

A thing to note though, not all places with large cloud mass means that they have been affected by cloud invigoration. In Singapore, we often find huge amounts of clouds in the skies but they are not necessarily or entirely caused by aerosol pollution, because Singapore lies in a belt of convective zone along the equator that promotes air uprising and convective cloud formation.

Glossary of terms: 

Aerosol forcing: Effect of aerosol on the climate, particularly anthropogenic aerosols and how they affect radiative fluxes in the atmosphere. In simplest layman terms, effects of aerosols are quantified as causing increase or decrease in atmospheric temperature. 

Positive feedback: Refer to this page here

Cloud invigoration: A positive feedback in the formation of clouds, whereby larger cloud mass tends to attract more water vapour condensation, causing the clouds to gain larger mass and become larger and thicker clouds. 

Aerosol loading: Increase in concentration of aerosols in the atmosphere

Longwave and shortwave radiation: Refer to this page here



Koren, I., Dagan, G. and Altaratz, O. (2014). From aerosol-limited to invigoration of warm convective clouds. In: Science. 344(6188). pp. 1143-1146. [Online]. Available from: http://www.sciencemag.org/content/344/6188/1143.abstract.

Chung, C. E. (2012). Aerosol Direct Radiative Forcing: A Review. In: Abdul-Razzak, H. (ed). Atmospheric Aerosols – Regional Characteristics – Chemistry and Physics. [Online]. Available from: http://www.intechopen.com/books/atmospheric-aerosols-regional-characteristics-chemistry-and-physics/aerosol-direct-radiative-forcing-a-review