World's 10 cleanest cities

Mercer, the global financial and HR consulting firm, recently came up with a list of world's cleanest cities. Mercer took into account the air quality for the upkeep of streets and squares to produce the 2011 rankings.

Here are the ten cleanest cities in the world:

1. Calgary (Canada)

Calgary is positioned on 'the fringe of Canada's largest energy belt and enjoys lower taxes and less stringent regulations', says the Forbes study.

Calgary's economy is also dominated by oil and gas industry, apart from manufacturing and services.

Calgary, which boasts of impressive infrastructure, is well placed to be one of the fastest growing urban centres in the world.

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2. Honolulu (Hawaii, USA)

Honolulu is the capital of and the most populous census-designated place in the American state of Hawai.

Honolulu has a warm semiarid climate and enjoys warm weather and plenty of sunshine throughout the year.

Despite its location in the tropics, the climate (temperature, precipitation and humidity) is moderated by Hawaii's mid-ocean location.

The industries located in this region are very light and non-polluting.

An excellent bus transit system, has decreased the exhaust and traffic fume levels.

The proximity to the ocean also helps keep the city clean.

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3. Ottawa (Canada)

The second city from Canada to make it to the list of the Top 10, Ottawa -- at rank 4 -- has one of the best volunteer programmes to keep the city green and clean.

The Canadian capital of Ottawa has a humid continental climate with an extreme range in temperature.

Ottawa hosts a variety of annual activities -- most notable being the Winterlude Festival on the Rideau Canal in the winter and the National Canada Day celebrations on Parliament Hill in July.

During their Spring Cleaning the Capital month between April 15 and May 15, over 60,000 volunteers are present to clean the parks, roads and sidewalks etc of the city.

Like other green cities, Ottawa residents rely on a good light rail transport system to commute, thereby reducing the fumes in the city.

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4. Helsinki (Finland)

Helsinki is the capital and largest city in Finland.

It is Finland's major political, educational, financial, cultural and research centre.

Approximately 70 per cent of foreign companies operating in Finland have settled in the Helsinki region.

In 2009, Helsinki was chosen to be the World Design Capital.

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5. Wellington (New Zealand)

Wellington is the capital city and third most populous urban area of New Zealand.

The Wellington urban area is the major population centre of the southern North Island, and is the seat of the Wellington Region -- which in addition to the urban area covers the Kapiti Coast and Wairarapa.

The urban area includes four cities: Wellington City, on the peninsula between Cook Strait and Wellington Harbour; Porirua City on Porirua Harbour to the north; Lower Hutt City and Upper Hutt City.

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6. Minneapolis (USA)

Minneapolis, nicknamed 'City of Lakes' and the 'Mill City,' is the county seat of Hennepin County, the largest city in the US state of Minnesota, and the 48th largest in the United States.

Known as the 'Twin Cities,' Minneapolis-St. Paul is the 16th-largest metropolitan area in the United States, with 3.5 million residents.

Its name is attributed to the city's first school teacher, who combined mni, the Dakota word for water, and polis, the Greek word for city.

The city is abundantly rich in water with over twenty lakes and wetlands, the Mississippi river, creeks and waterfalls, many connected by parkways in the Chain of Lakes and the Grand Rounds Scenic Byway.

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7. Adelaide (Australia)

Adelaide is the capital and most populous city of the Australian state of South Australia, and is the fifth-largest city in Australia.

Named in honour of Queen Adelaide, the German-born consort of King William IV, the city was founded in 1836.

It is known as 'The City of Churches'.

Adelaide has an estimated population of more than 1.28 million.

Adelaide is a coastal city situated on the eastern shores of Gulf St Vincent, on the Adelaide Plains, north of the Fleurieu Peninsula, between Gulf St Vincent and the low-lying Mount Lofty Ranges.

The suburbs reach roughly 20 km (12 mi) from the coast to the foothills but sprawl 100 km (62 mi) from Gawler at its northern extent to Sellicks Beach in the south.

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8. Copenhagen (Denmark)

Copenhagen is the capital and largest city of Denmark situated on the islands of Zealand and Amager.

Copenhagen has repeatedly been recognised as one of the cities with the best quality of life.

It is also considered one of the world's most environmentally friendly cities.

The water in the inner harbour is so clean that one can swim in it, and 36 per cent of all citizens commute to work by bicycle.

Every day they cycle a combined 1.2 million km.

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9. Kobe (Japan)

Kobe is Japan's sixth-largest city and is a great holiday destination.

Hot springs of Arima Onsen, Ikuta Shrine and Kobe Port Tower, which provides stunning night views of the city are some of the hottest tourist destinations.

Prefecture on the southern side of the main island of Honshu, approximately 500 km (310.69 mi) west of Tokyo.

Kobe is a prominent port city.

The city is located in the Kansai region of Japan and is part of the Keihanshin metropolitan area along with Osaka and Kyoto.

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10. Oslo (Norway)

Oslo is the world's most expensive city.  It is the capital and the largest city in Norway.

Founded around 1048 by King Harald III of Norway, the city was largely destroyed by a fire in 1624.

The Danish Norwegian king Christian IV rebuilt the city as Christiania (briefly also spelt Kristiania).

In 1925 the city reclaimed its original Norwegian name, Oslo.

Oslo is the cultural, scientific, economic and governmental centre of Norway.

The city is also a hub of Norwegian trade, banking, industry and shipping.

It is also an important centre for maritime industries and maritime trade in Europe.