More than dust in Delhi

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smog in delhi
The smog over Delhi. Photo credit: Jean-Etienne Minh-Duy Poirrier / Creative Commons

Urbanization provides the countries of South Asia with the opportunity to transform their economies to join the ranks of richer nations. But to reap the benefits of urbanization, nations must address the challenges it poses. Growing urban populations put pressure on a city’s infrastructure; they increase the demand for basic services, land and housing, and they add stress to the environment.
 
Of all these congestion forces, one of the most serious for health and human welfare is ambient air pollution from vehicle emissions and the burning of fossil fuels by industry and households, according to the World Bank report, Leveraging Urbanization in South Asia: Managing Spatial Transformation for Prosperity and Livability.”
 
Particularly harmful are high concentrations of fine particulate matter, especially that of 2.5 microns or less in diameter (PM2.5). They can penetrate deep into the lungs, increasing the likelihood of asthma, lung cancer, severe respiratory illness, and heart disease.
 
Data released by the World Health Organization (WHO) in May 2014 shows Delhi to have the most polluted air of any city in the world, with an annual mean concentration of PM2.5 of 152.6 μg/m3 . That is more than 15 times greater than the WHO’s guideline value and high enough to make Beijing’s air—known for its bad quality—look comparatively clean.

But Delhi is far from unique among South Asia’s cities.

In a global sample of 381 developing-country cities analyzed in the report, 19 of the 20 with the highest annual mean concentrations of PM2.5 were in South Asia. And the issue is not just in India—Karachi, Dhaka, and Kabul all feature in the top 20.

Controlling for factors like climate (levels and variability of rainfall and temperature) and geography (such as distance to the coast), analysis of the data shows that, for developing-country cities globally, annual mean concentrations of PM2.5 are positively and significantly correlated with both city size and population density within a 20-kilometer radius of the city center. Although these relationships are expected, they are stronger in South Asian (SAR) cities for population density than in other developing-country cities (see figure below). In developing-country cities outside South Asia, a doubling of population density is associated with a 24.2 percent increase in PM2.5, but in South Asian cities the increase is 34.8 percent.

Relationship between annual mean concentration of PM2.5 and city population density for 381 developing-country cities


 
Relationship between annual mean concentration of PM2.5 and city population density for 381 developing-country cities

So, what accounts for this uniquely strong impact in South Asian cities?
 
More research is needed, but it seems plausible that the answer lies in the relationship between a city’s population density, the number and spatial configuration of potential pollution sources within or near a city, and the volume of pollution emitted by each source. For example, given failures in planning, one can speculate that an increase in population density is associated with a greater probability of traffic gridlock in South Asian versus non–South Asian cities, contributing to a higher relative increase in air pollution. It’s also possible that, for South Asian cities, a given increase in population density could be associated with a proportionally larger increase in forms of economic activity that rely on dirty forms of energy. For example, small- and medium-sized enterprises all typically rely on dirty energy forms in developing countries.
 
Tackling the problem requires policy responses—and quickly.
 
Indian cities have been known to battle air pollution successfully in some places and at particular times.  Despite these measures, however, most cities are losing the war.
 
A new wave of pollution control initiatives is needed. These measures will have to range from further improvements in fuel quality and vehicle technology to greater access to public transport and changes in patterns of urban development to reduce the need for transport, as well as switching industries and households to cleaner fuels. Indian cities will also need to improve air quality monitoring to get a better handle on the extent of the problem and to invest in source apportionment studies to better understand pollution sources.
 
To read the report, go to: www.worldbank.org/southasiacities.

FOUZIA RAHMAN
October 30, 2015

Life in a City of South Asia is quite interesting and addictive especially the city where you are born, raised and had education. I was born and raised in Karachi which has changed over the last few decades in both positive and negative sense. Today there are modern shopping malls, cinemas, 5 star hotels, designer boutiques and restaurants. But I miss clean air, 24 hours water supply, sense of security in public places and roads. Karachi is now ranked as 5th polluted city in terms of air quality in South Asia and in terms of livability it is ranked 135 out of 140 South Asian cities. Despite all this when my plane lands at Karachi airport it is homecoming that I rejoice.

Mark R
November 02, 2015

Thank you for this insight into life in Karachi. What you describe captures perfectly the tension between, on the one hand, the positive benefits associated with urban density and the negative "congestion" effects (or what Edward Glaeser refers to as the "demons of density"). Making cities more prosperous and livable requires cultivating the benefits, while also undertaking actions to ease congestion pressures on infrastructure, basic services, land, housing and the environment. We discuss this in more detail at www.worldbank.org/southasiacities

Joshua Apte
November 07, 2015

2 factors explain the data.
First: meteorology. Atmospheric mixing across the Indo-Gangetic basin (spanning very roughly from Karachi to Islamabad to Delhi to Dhaka) is substantially weaker than in many places in the world. For a given unit of emissions, higher atmospheric concentrations will result.
Second: high per-capita PM emissions. Although per-capita energy use is low S. Asia, emissions per unit of delivered energy service are very high. Vehicle emissions per km are high. More importantly, S. Asian cities have large populations that rely on solid fuels for cooking and heating. Autumn and wintertime burning of wood and wastes for heat and waste management result in exceptionally high seasonal-average PM concentrations.
There is a silver lining in this story. The phenomenon you observe in these data is closely linked to the concept of intake fraction: the proportion of pollutant emissions that are ultimately inhaled by an exposed population. Intake fraction is higher in large South Asian cities than nearly anywhere else. (See this journal article: http://pubs.acs.org/doi/abs/10.1021/es204021h). This is bad news as long as emissions remain high. The good news? When emissions are reduced, the population exposure benefit will be especially high in cities with high intake fractions. Thus: cities in South Asia stand to gain disproportionately high exposure and health benefits for each unit of emissions reduction.
Great blog post, by the way, Mark and Urvashi. Thanks!

George
October 28, 2015

Climatic factors may also be relevant. For example: Higher temperatures result in greater ozone formation. There may be lower average wind speeds in the tropics increasing pollution levels, but also more frequent rainfall which removes air pollutants.

Mark R
October 29, 2015

Many thanks for your comment George! We agree that climatic factors can be important determinants of air quality. Indeed, in our analysis, we control for climatic factors, including the degree and variability of rainfall. What is interesting is that the relationships we report in the blog between pollution outcomes and population size/density exist even holding these factors constant. It seems that, at a given population density, pollution outcomes (especially for big cities) are worse in South Asian versus non-South Asian developing country cities. The next key question that needs investigating is that of exactly why this might be the case?

Ulrich
October 28, 2015

Good write-up, but you could have given one additional source of air pollution some prominence: dysfunctional solid waste collection means household garbage is incinerated at intersections in major cities. Hardly compatible with pollution control.

Mark R
October 29, 2015

Many thanks for your comment! This is a good observation with which we agree. More generally, more detailed research is required to better understand the exact contributions made by different pollution sources within (and nearby to) cities, and exactly what mechanisms underlie the stronger relationship between PM2.5 levels and population density in South Asian versus non-South Asian developing country cities

Ama Forson
October 28, 2015

Dear Urvashi, this is very informative and brings fresh insights to an issue that somewhat is glaring to the naked eye and which seems to be lingering on but with hopeful prospects for an integrated actionable solutions.
What are your views about taking forward integrated solutions like you outline that would involve a couple of sectoral actors - from transport, energy and environment?
In some sense, some clients may feel that 'enough' studies have been carried out already to inform the urgency of the situation and so what is needed is action (some iota of truth if you would allow me to play devil's advocate here) so what would really get the wheels off the ground in tackling the air quality battle?
Thank you again for the fresh insight!

Mark R
October 29, 2015

Many thanks for your comment Ama and also for playing devil's advocate! It is indeed true that many studies have already been carried out to inform the urgency of the situation re. air pollution in South Asian cities. However, we still don't really understand the relationships between spatial form and air pollution outcomes, and so there remains a need for more research in this area. Furthermore, new studies can help to re-invigorate the interest of policymakers and keep the issue in the public eye. At the same time, we do acknowledge that it is equally important, as you say, for studies to ultimately inform action.

Prateeksha S
November 06, 2015

I would like to help in the research. Hoping you have ideas on how to go about it, and whom to collaborate with. I'm a software engineer who has worked in Bangalore and the US. I have now taken up the initiative of raising air pollution awareness locally, as well as, online. Breathe Better (https://www.facebook.com/groups/whiffs/) is the Facebook group I moderate for this purpose.
www.linkedin.com/in/prateekshasatyamoorthy