On a recent rainy Sunday morning in a Mexico City neighborhood, people lined up under their umbrellas with bags of empty milk cartons, plastic bottles and cardboard at their feet.

The rain did nothing to dampen their enthusiasm for the Mercado de Trueque, or barter market, where recyclable materials are exchanged for points then used to buy organic food and products.

"It's great because a lot of the time one doesn't know what to do with all of this stuff and I think it's really irresponsible to just throw it away," said Maria Fernanda Vasquez, a photographer huddled under an umbrella with her friend Mina Moreno.

Moreno added: "We need to give a little something back to Mother Earth."

The Mercado de Trueque is among a slew of green initiatives that have been launched by the capital's left-wing government in recent years to clean up this smoggy metropolis of 20 million people, which was considered the world's most polluted city some 20 years ago.

The monthly market, which was inaugurated last year, aims to raise awareness about the value and use of items that would otherwise end up in landfills, and is growing in popularity in a city that generates more than 12,000 tonnes of trash per day.

The recyclables brought to market by people are weighed by an army of apron-wearing helpers, and then heaped onto waiting trucks to be transported to a local recycling company.

Market-goers are rewarded with green points, a bespoke currency, depending on the quantity of materials they bring in. They then take their points next door to a produce market to spend on food and other products on sale.

The scheme means no one goes away empty-handed after bringing their trash in for recycling. It was the first time Andrea Gutierrez and her boyfriend Alan Riestro came to the market loaded with newspapers and plastic bottles.

"We bought radishes and cottage cheese, and still have 40 or 50 pesos ($3 or $4) left to spend," said Gutierrez at a recreational center within the site of the 1968 Olympic village.

Local producers also benefit. They sell all of their produce to the government, and then bring them here for exchange.

Pedro Jimenez, a local producer who was manning his stall of cauliflowers, said: "It's good for us because the government pays above the normal market price (for our products)."

Last year the project collected more than 170,000 tonnes of recyclable materials.

The city government overhauled waste management in 2011, requiring people to separate organic and non-organic trash and closing an enormous landfill that received 6,000 tonnes of trash per day.

The barter market is another effort at sorting trash. It accepts a wide range of materials for recycling, from the obvious cardboard and glass to electric appliances such as old typewriters and computers that no longer work.

At least 2,000 people come to the event every month, which rotates around different locations throughout the city. Enthusiasm for the concept is such that queues here are often long and slow.

There have been complaints that people are forced to wait hours in line to do their good deeds.

"A lot of people come. The aim of the market is to help people to understand their trash has a value and to separate the materials," said Liliana Balcazar, a government worker who helps organize the market.

"It's not to solve the recycling problems of the city - that's very complex and the demand for the market grows each month," she said.