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September 2011 Archives

Biomass limits (Part 2)

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Liquid biofuels for transport, but also other types of biomass production and use, have been promoted as away to reduce greenhouse gas emissions, boost rural development and ensure energy independence. However this approach has run up against major constraints, including land-use and biodiversity issues. Moving to second generation non-food biofuels, and also biomass wastes, may help, as may tighter regulation (see my previous Blog

But there may also be clever approaches that avoid some of the land-use limits of biomass.

Perhaps the most obvious is to use biomass differently. Biogas production via anaerobic digestion (AD), e.g. of bio wastes, is widely seen as a good idea - coupled with using the gas grid for delivery. You can then use it for heating. But you can also use biogas in car engines. For example, it's been claimed that methane through AD requires only about a quarter of the land area ethanol requires, and is a far more efficient fuel than ethanol, easily used in cars and trucks. There are certainly enthusiasts for it in the UK and elsewhere: and\%27%3Fiframe%3Dtrue

Another option is to produce hydrogen by thermo-chemical processing of biomass/wastes, as proposed by Karl-Heinz Tetzlaff, possibly combined with CCS.

The hydrogen can be used for heating, possibly admixed with methane and delivered via the gas main; in fuels cells; or as a vehicle fuel direct. Or it can be used to make syngas /ammonia.

There are however some efficiency penalties involved with these various conversions. A PhD thesis by Anna Suess from Eindhoven Technical University looks at biomass as a CO2 saving technology. She compared synthetic natural gas (SNG), methanol, Fischer-Tropsch fuels, hydrogen and bioelectricity. Although she concludes that the overall practical resource is limited, the best option evidently proved to be converting biomass into electricity and using that to power electric cars. 'First of all, biomass can be converted efficiently into electricity. Electricity can also be generated in smaller plants, which reduces the need for transport. And finally, electricity is a clean and efficient energy source for vehicles'. That certainly fits with the current vogue for an all-electric green energy future with cars run of electricity from renewable sources, but whether bio-conversion is better than electrolysis (e.g. using wind generated electricity) is far from clear- although you can store biomass.[ttnews]=10544&txttnews[backPid]=926&cHash=5464e54533

However there are also more radical approaches. For example , "Breaking the Biomass Bottleneck", a report by Henrik Wenzel (from Concito, a green 'think tank' in Denmark), suggest that we could upgrade biomass by hydrogenation, using hydrogen produced by the electrolysis of water, powered by excess electricity from variable renewables like wind. The report claims that you can react biomass with hydrogen 'to produce hydrocarbons of much higher energy content and energy density than the original biomass. Moreover, using the biomass and the biogenic carbon from hydrogenation in central applications like heat and power , it is possible to collect the CO2 from the biomass and further recover and recycle it in a process here called Carbon Capture and Recycling, CCR. This will further multiply the use of the biogenic carbon from the biomass. Overall, upgrading and recycling biogenic carbon by hydrogenation and CCR, can approximately five-double our biomass potential for providing storable and high-density fuels and carbon feedstock compared to the presently applied technologies for converting biomass to fuels and feedstock.'

This sound wonderful- something for nothing, although, not really, since it can't invalidate the laws of thermodynamics. But, the report notes, even with electrolysis losses, 1 Joule of wind can save 1 Joule of biomass, by upgrading it. However, the report adds 'The total energy content of the biomass and the hydrogen is, of course, greater than that of the fuels on the output side. If, therefore, hydrogen is sufficiently good for the demanded energy services in question, there is no sense in taking a detour of producing the carbon based fuels from the hydrogen. The conversion from hydrogen to carbon fuels as energy carrier is only justified by the inherent differences in the properties and qualities of the two'.

So it's end-use utility that matters, especially as it costs more, given the efficiency loses. But even so, the report claims that it makes sense. Not only go you get a valuable green fuel, you can also store it easily and help balance variable wind and other renewables, while using less biomass and less land. Moreover, if the biomass used is replaced consistently and sustainably, and you capture the CO2 produced when the fuel is burnt, then you have an overall net carbon negative system- although the report says that transport uses are less attractive, since then you can't capture the CO2.

There are also versions of this idea which just use hydrogen produced from wind derived electricity and carbon dioxide from the atmosphere, to generate methane, methanol or some other synfuel. See for example

It would in effect create a carbon neutral fuel from the movement of and COs in the air, and it could be carbon negative if the CO2 was collected after combustion. Moreover, it avoids biomass land-use issues entirely. However air capture of CO2 still remains very expensive, so biomass looks a more likely carbon feedstock for the moment.

All in all though, there's some clever green chemistry emerging. For more see:]

Another very ambitious approach involves using algae, or other biomass, grown in desert areas, possibly coupled with CCS. It's been argued that, if algae is grown at the yields that the IEA Task Force bio-energy says is credible, then a land area the size of 24 % of Australia (in practice spread around Earth's deserts) would produce 90,000 TWh/y which nearly equivalent to the current global final energy demand of 98,000 TWh/y. Moreover if some of that algae /biomass is used in CCS schemes then we would have a powerful carbon-negative energy technology: BECCS - bio-energy with CCS.

The Global CCS Institute has just produced a report which concludes: 'there is a widespread unawareness of BECCS amongst policy makers, and also a lack of research and demonstration programs directed at the BECCS segment of climate mitigation measures. The insufficient efforts in research and deployment of BECCS are detrimental not only for the biomass industries, but for climate mitigation policies in general. Studies show that billions and trillions of Euros could be saved by including BECCS in mitigation portfolios. There are also large benefits to be gained in developing joint transportation and storage systems for fossil fuel CCS and BECCS, as this would increase economies of scale and lower the costs'.

One way to do this might be by growing algae in a Seawater Greenhouse As I've noted before, the first commercial SG scheme is up and running in Australia and more are planned around the world, possibly in conjunction with CSP technologies, to desalinate water. See

For food or algae production, as well as energy and water, you have to provide nutrients. One way to do this might be to stir up the sea-bed near the water entry point and suck in the sediment, then filter and dry it. Of course there are many uncertainties in relation to, for example, costs and impacts on fragile desert and marine ecosystems. However, the Dutch routinely use ocean sediment, allowing the saline content to drain back to the sea. Clearly, if this is to be done on any scale, we will need some detailed Life Cycle Assessments first. See

Certainly many 'greens' are worried about the use of biofuels to keep the cars (and planes) going for a range of reasons.. See for example: and

Moreover, in terms of electricity and heat production, many would see conventional flow renewables, like solar, wind, wave and tidal power, as a better bet, with fewer eco impacts: e.g. see Mark Delucchi's biomass LCA studies: Ann. N.Y. Acad. Sci. 1195 (2010) 28-45 and Biomass and Bioenergy (2010), doi:10.1016/j.biombioe.2010.11.028

The debate continues, with the latest input being a fairly critical report from the RSPB: 'Bioenergy: A Burning Issue', which says the rush to build new power stations in the UK will mean that imports of the wood needed will have to rise from 13% to 68%- three times higher than the UK's total current wood production.

Biomass limits (Part 1)

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An 18-month inquiry by the independent Nuffield Council on Bioethics (NCB) has found that rapid expansion of biofuels production in the developing world has led to problems such as deforestation and displacement of indigenous people. The need to meet rising biofuel targets has also led to exploitation of workers, loss of wildlife and higher food prices. Biofuels also contribute to poor harvests, commodity speculation and high oil prices which raise the cost of fertilisers and transport. However, it says, there is a clear need to replace liquid fossil fuels to limit climate change and if new biofuel technology can meet ethical conditions, there is a duty to develop it.

NCB say an international certification scheme, like the Fairtrade scheme for food, was needed- to guarantee that the production of biofuels met the five ethical conditions identified by the NCB: observing human rights, environmentally sustainable, reduced carbon emissions, fairly traded and equitably distributed cost and benefits.

In a new report, the Food and Agriculture Organization of the United Nations (FAO) similarly claimed that bioenergy could be part of the solution to climate-smart agricultural development, but only if their production was properly managed. Large-scale liquid biofuel development, in particular, may, they say, hinder the food security of smallholders and poor rural communities, and enhance climate change through greenhouse gas (GHG) emissions caused by direct and indirect land use change. It's therefore crucial they say to develop bioenergy operations in ways that mitigate risks and harness benefits. Safely integrating both food and energy production addresses these issues by simultaneously reducing the risk of food insecurity and GHG emissions, and Integrated Food-Energy Systems (IFES) can, they claim, achieve these goals on both small- and large-scales.

This may sound like wishful thinking, but FAO offers concrete options for how smallholder farmers and rural communities, as well as private businesses, could benefit from these developments and attempts to give a holistic picture of the different types of energy that can be produced from agricultural operations, and how they can be aligned with current food production schemes.

The International Energy Agency similarly seems convinced that, given proper controls, biofuels can play a major role. In its new Roadmap, it says that they could supply 27% of global transport fuel by 2050, on a sustainable basis. The IEA says that 'while vehicle efficiency will be the most important and most cost-efficient way to reduce transport emissions, biofuels will still be needed to provide low-carbon fuel alternatives for planes, marine vessels and other heavy transport modes'. With optimised policies in place, the report predicts that biofuel production could grow from 55 million tonnes of oil equivalent (Mtoe) today to 750 Mtoe in 2050.

To protect land for food production, the IEA suggests using 1 billion tonnes of residues/wastes, and 3 billion tonnes high-yielding non-food energy crops, the so-called second-generation technologies, such as cellulosic ethanol. Even so, production would have to be supplemented with around 100m hectares of land - around 2% of total agricultural land, a three-fold increase compared with today. And the report admits that the 27% target is only attainable if lignocellulosic technologies are produced at an industrial scale within 10 years, and would require government support and research and development investment of more than $13 trillion over the next four decades and an international support programme. But it was claimed that 'biofuels would increase the total costs of transport fuels only by around one per cent over the next 40 years, and could lead to cost reductions over the same period.'

The report warns that the use of fossil energy during cultivation, transport and conversion of biomass to biofuel will have to be reduced, while direct or indirect land-use changes, such as converting forests to grow biofuel feedstocks which release large amounts CO2, must be avoided. The IEA says that it is important to impose sustainability standards for biofuels to prevent harmful impacts on land, food production and human rights. It suggests a land use management strategy be imposed along with a reducing in tariffs to encourage trade and production of biofuels.

Are these proposals realistic? It ought to be possible, at least in theory, given the right regulatory framework, to avoid food-energy conflicts, but even with the best technology, there's still a risk that commercial pressures, locally and globally, for high added value vehicle fuel production will overwhelm any efforts at balance and integration- energy is the ultimate cash crop. For example, not all of it is for vehicles, but only 6% of the current global supply of palm oil meets sustainability standards: see:

If we move away from high added-value products like biofuels for transport, the situation gets a little easier. Biomass can also be used for heat and power. Indeed many argue this make more sense- since the final energy yields/acre using solid woody biomass are generally higher than for liquid biofuel production.

The Potsdam Institute for Climate Impact Research (PIK) has looked at the overall global potential for biomass and concluded that it could meet up to 20% of the world's energy demand in 2050, half of it from biomass plantations. But that would involve a substantial expansion of land use, by up to 30%, depending on the scenario, and irrigation water demand could double.

In the PIK study, fields and pastures for food production were excluded, as were areas of untouched wilderness or high biodiversity, as well as those forests or peatlands, which store large amounts of CO2. But with second generation (non food) energy crops, the bioenergy potential ranged from 25 to 175 exajoule by year: the lower outcomes are for strong land use restrictions and without irrigation, the higher outcomes assume few land use restrictions and strong irrigation.

A middle scenario would result in about 100 exajoule, while the world's energy consumption is estimated to double from today's 500 to 1000 exajoule by 2050. It's claimed that roughly the same amount of energy production, in addition to biomass plantations, could result from agricultural residues. Hence the 20% headline figure, with increased use of residues instead of cultivating dedicated energy crops seen as crucial for a sustainable future.

Beringer, T., Lucht, W., Schaphoff, S.: Bioenergy production potential of global biomass plantations under environmental & agricultural constraints. GCB Bioenergy, 2011 [doi:10.1111/j.1757-1707.2010.01088.x]

A new study funded by the UK Energy Research Centre (UKERC) came to similar conclusions, at least on the benefits of using non-dedicated land, in the UK context. It looked at the potential of planting short rotation coppice (poplar and willow) in England, taking into account social, economic and environmental constraints and concluded that planting short rotation coppice energy crops on England's unused agricultural land could produce enough biomass to meet renewable energy targets without disrupting food production or the environment.

The UKERC study, published in Biofuels, says that new technology will enable bio-fuels to be made from lignocellulosic crops (e.g. short rotation coppice willow and poplar), which, unlike current cellulosic crops (typically derived from food crops such as wheat and maize) can grow on poor-quality agricultural land. While the results suggest that over 39% of land in England cannot be planted with SRC due to agronomic or legislative restrictions, marginal land (ALC grades 4 and 5) is realistically available to produce 7.5 m tons of biomass. This would be enough to generate approx 4% off current UK electricity demand and approx 1% of energy demand. The SW & NW were seen as having the potential to produce over one third of this, owing to their large areas of poor grade land.

Not everyone will agree that, even with new types of crop, biomass can be much of an options, but in Biomass limits 2, next week, I'll be looking at some radical technical fixes that might improve the situation for biofuels and/or biomass use.

Tllting at offshore wind

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Offshore wind is moving ahead rapidly in the UK. There is 1.5GW in place, over 2GW in construction and 1.7GW with approval. And DECC now says that up to 18GW could be installed by around 2020.

So far most of the projects have been in English waters, but now projects are planned off Scotland. However objections have begun to emerge- and have attracted media attention. For example, US tycoon Donald Trump has criticised a proposal to build an 11 turbine offshore wind farm in Aberdeen Bay near his golf resort. He said he would use all legal means to oppose it.

Perhaps more significant have been the objections to the much larger project proposed by ScottishPower Renewables, who want to build a 180 turbine offshore windfarm 5km off the southwest coast of Tiree in the Hebrides. This 'Argyll Array', has met with strong local opposition. The No Tiree Array group want it put much further out. But that would be in deeper water, and need longer undersea grid links, adding substantially to the cost. .

Visual intrusion is obviously a concern when projects are near shore, but anti-wind project groups have also been moving on to economic viability: e.g. see

BBC Radio News has been running a series on offshore wind, asking if they were 'an expensive luxury', which included coverage of Oxford Prof. Dieter Helm's view that, while the government should invest in green power, offshore wind farms are far too expensive.

The Daily Telegraph (14/6/11) made much of a National Grid report which noted that by 2020 it was expected that wind generation output might have to be 'curtailed' on about 38 days per year, because of excess production over need. The Telegraph commented 'some experts believe this will cost almost £300m a year by 2020, with the cost passed on to consumers'. However tucked away at the end of the article was a quote from a grid spokesman, who said: 'Over the past year we have had to reduce output from wind generators on 25 days, amounting to less than half of one per cent of the output of wind generation connected to the high-voltage transmission system over the same period.' Moreover, new grid balancing, storage and load management techniques should improve e.g. wind forecasting techniques, making it easier/cheaper for gas turbines to load follow: /Media+Centre/PressReleases/2011/25.05.11+wind+forecasting.htm

Even so, the Telegraph seemed convinced that wind power was a poor option It subsequently quoted from a new report from the Oxford Institute for Energy Studies which had concluded that 'the maximum feasible level of wind generating capacity is 28 GW. At higher levels than this, the country faces the prospect of short notice intervention to reduce turbine output with the added complication that forecasts of wind speed beyond six hours into the future are inherently uncertain.' The report commented 'It would appear that the more ambitious targets for wind generation in the UK have been formulated without a full appreciation of the costs and complexities caused by the intermittency of very substantial levels of wind generation'.

In a more nuanced report from the Cambridge University Electricity Policy Research Group, Prof. John Newbery argues that the main economic problem is likely to be due to the support mechanism planned for future projects- the proposed variable-price market-based 'Contracts for a Difference' (CfD) system . He says that the CfD could lead to over £250m of electricity consumers' money being wasted every year, and rising, as offshore wind develops. He argues that 'a CfD on metered output will still leave basis risk and volatility risk (having to contract ahead of knowing actual output) on the wind developers, while a classic fixed FiT would transfer all those risks to an agency better placed to bear them, and at lower cost. The financial benefits of this risk reduction and reduced cost of capital for on-shore wind alone might together be £250m per year by 2020... and perhaps £70m p.a by 2020 for on-shore wind'.

There clearly are risks in developing new projects like off shore wind farms. The Crown Estate has just ended an agreement to buy the first 10MW Britannia offshore wind prototype from Clipper Windpower, after Clipper's parent company, United Technologies Corporation (UTC), halted the project. It was to have been built in Newcastle.

However, it is not all bad news for offshore wind. Siemens, Vestas, Gamesa, GE and Doosan still plan to manufacture large offshore turbines in the UK. Moreover, there have been some very positive reports on environmental impacts. As the Guardian reported, a Dutch study has concluded birds avoid offshore wind turbines, while marine life finds shelter and new habitats, so that, overall, offshore wind turbines have "hardly any negative effects" on wildlife, and may even benefit animals living beneath the sea. The researchers studied a wind farm near Egmond aan Zee, off the Dutch North Sea coast.

Prof. Han Lindeboom from the Institute for Marine Resources and Ecosystem Studies at Wageningen University said 'At most, a few bird species will avoid such a wind farm. It turns out that a wind farm also provides a new natural habitat for organisms living on the sea-bed such as mussels, anemones and crabs, thereby contributing to increased biodiversity. For fish and marine mammals, it provides an oasis of calm in a relatively busy coastal area'.

The researchers noted that the turbines help to protect schools of cod, and that porpoises are heard more often inside than outside the wind farm. The survey also concluded that sea bird species such as gannets tend to avoid the turbines, while seagulls appear unflustered and local cormorant numbers even increased.

The study noted that, depending on their position, offshore wind farms can contribute to a more diverse habitat and even help nature to recover from the effects of intensive fishing, pollution, oil and gas extraction, and shipping. But it recognised that the rotating blades can have a 'disruptive impact' on some bird species, and recommends that wind farms are located to minimise possible impact.

Meanwhile, the Guardian reported, with a major offshore wind programme planned, Germany, is looking to 'soundproof' offshore wind underwater construction sites to protect whales and porpoises in Baltic from the noise from pile driving- by installing pipes on the sea bed to produce a 'bubble curtain' to absorb the sound.

Green energy policies mean 'more pain than gain' for the UK, according to a new Civitas report 'Green Mirage' by Dr John Constable, director of policy and research at the Renewable Energy Foundation (REF). He claims that the low-carbon economy will not deliver many jobs in the UK. He reviews a series of economic models developed for the EU Commissions 2009 EmployRES, which, he notes, predicted that the EU-27's s climate policies will have only 'slight' net positive benefits in terms of GDP and net employment by 2020. He points out that this outcome assumes that Europe remains dominant in the world export markets for low-carbon technologies, whereas, the experience of competition between the German and Chinese solar industries does not support this view. Basically China came up with cheaper solar cells and dominated the market.

Moreover, any EU gains will be unevenly spread, with the UK missing out. For example, Spain was the main winner on most of the Commission's optimistic export scenarios gaining an estimated 120,000 net jobs via current green policies, and over 150,000 if green subsidies are accelerated. But the UK loses 10,000 jobs with current green policies and 30,000 jobs if those policies are accelerated with more subsidies. Basically, he adopts a traditional free market view, and argues that, the more green technologies are subsidised by the EU, the greater the predicted net loss for British workers.

He and REF are have been very hostile to subsidies. He notes that in the period 2002-2010 the UK spent £5 billion subsidising dedicated renewable electricity generators, at a cost of £230,000 per wind industry worker. He says that the subsidy per wind industry worker in the year 2009/10 amounted to £54,000, which is greatly in excess of the median earnings in either the public (£29,000) or the private sectors (£25,000).

Challenging the approach taken by the Campaign against Climate Change, in their booklet 'One Million Jobs', he claims that continuing to subsidise renewables will not only result in net job losses, it will also impose high costs on the rest of the economy, undermining international competitiveness. A subsidised artificial market for low-carbon industries will provide a 'premature reward for unready technologies', and actively discourage further invention. He claims that current green policies waste resources that could be better spent on improving low-carbon technologies for the future.

As a result, 'Far from re-energising Britain's economy, the 'green economy' will drain investment from other sectors, making Britons pay more for electricity indefinitely and live less productive lives with access to fewer jobs'.

In response, trade lobby RenewablesUK (RUK) said that the figures used by Constable were not a reliable guide to the future - so far the UK had focused on on-shore wind using imported technology, whereas now, investment was expected to be directed more towards off-shore wind. 'A lot of the calculations seem to be based on what's happened in the past - we are looking at the future. Britain is set to be a market leader in offshore wind.'

The hope is that more of the resultant jobs will created in the UK- as a result of inward investment in new manufacturing facilities. RUK says "The potential for job creation is phenomenal If you take onshore, offshore and the associated supply chains then by 2021 it's around 88,000 jobs in the UK. To be talking about a net loss of jobs is not borne out by evidence' Constable is not impressed by this view- he suggest that, although some areas in the UK may benefit, the overall economic inefficiency of subsidies for renewables will lead to a net loss.

The numbers can of course be debated endlessly- econometrics is a complex and some might say unreliable science. But for example, the EC report which Constable refers to concludes that, if the EU can meet its target of getting 20% of its energy from renewables by 2020, that will provide a net effect of about 410,000 additional jobs and 0.24% additional gross domestic product (GDP). Note that this is net job gains- taking account of those jobs lost due to restructuring of the energy industry. If that really is the case, it is surely to be welcome, rather than, as Constable seems to think, being too small to matter.

Leaving the numbers aside, clearly there are some basic ideological differences in approach between Constable and those who look to renewables as part of the solution to both climate and economic problems, and in particular on the issue of subsidies. For example, Constable seem to see subsidies and innovation as being fundamentally opposed. That rather depends on your time frame. Subsides can be seen as investments in the future, helping new technologies and markets to develop, and that can lead to reduced costs longer term. But the risk is that the focus will just be on the near-market options, as with the Renewables Obligation- which was in any case very wasteful and inefficient. Thankfully it's now to be phased out. So Constable should be pleased. Rather than this approach, we need support for the less developed options, to help them move down their learning curves to lower costs. That's what the Feed In Tariffs have tried to do across the EU, with some considerable success in terms of wind power and also PV solar, although evidently that has not happened fast enough, in the case if PV solar, to avoid the charge that the FiT was passing to much cost on to consumers. So the PV FiTs have been cut back. Constable would not doubt be pleased, but if you want to push renewables on fast, you do have to provide extra support through some mechanism - just leaving it up to the market will not be enough.

It seems to be the case though that Constable does not want to push renewables fast, at least not the current ones, and not in the way that has been done so far. It is fair enough to have a debate on strategic choices. For example, REF has backed heat-producing renewables, as a better option than electricity generating micro-generation. But at times it is hard to follow REFs economic logic. For example in the past REF has been very critical of the support given to wind power, and has thereby evidently happily joined in with the anti-wind reaction. But more recently REF have backed offshore wind- despite that fact that this is much more expensive than on-land wind. Perhaps it has recognised that the resource is very much larger. And that costs will fall. Similarly for wave and tidal stream power. There is obviously plenty to debate when looking at which renewables to back, with REF clearly having its own views

However, in this new report, Constable seem to challenge the whole renewable energy project, at least as currently configured and supported. Presumably, if we are still to have a low carbon future, then that leaves us with slow development of renewables and more emphasis on low-carbon technology like Carbon Capture and Storage and nuclear power. That would be a somewhat odd recipe to be backed by an organisation called the Renewable Energy Foundation.


EmployRES Report:

CaCC booklet:

Air pollution is commonly measured with immobile detectors attached to buildings. Measured pollution levels do not necessarily relate to the impact of air pollution as experienced on the street. Josh Apte and colleagues addressed the question of air pollution as experienced by commuters by measuring concentration of pollutants in a transportation micro-environment, i.e. in a moving auto-rickshaw in New Delhi.

New Delhi, as other cities in rapidly developing countries, is plagued by chronic congestion and air pollution, producing massive social costs for its inhabitants.

The main results of this study are three-fold. First, measured exposure concentrations are higher in New Delhi than measured before in other megacities. Second, high short-duration peak concentrations, integrated over time of exposure, are a main culprit of the overall high exposure. Third, the total exposure of one commute in an auto-rickshaw approximately corresponds to the total daily exposure experienced by city inhabitants in rich countries.

While New Delhi switched its public bus fleet from diesel to clean natural gas, this seemed to not have been sufficient to reduce air pollution to acceptable levels. In fact, on-street air pollution is likely to even worsen because of increased vehicle ownership an on-going trend to diesel LDV.

The high costs and impacts of air pollution seem to warrant much tighter regulation of vehicle emissions also in developing countries. In addition, enforced parking management and a more comprehensive bus rapid transit system with dedicated bus lanes may not only benefit air quality but increase also transport efficiency.

Read also this blog here, and watch the video tracking on-street exposure.