found that recycling causes 35% less water pollution and 74% less air pollution than making virgin paper. Pulp mills can be sources of both air and water pollution, especially if they are producing bleached pulp. Modern mills produce considerably less pollution than those of a few decades ago. Recycling paper provides an alternative fibre for papermaking. Recycled pulp can be bleached with the same chemicals used to bleach virgin pulp, but hydrogen peroxide and sodium hydrosulfite are the most common bleaching agents. Recycled pulp, or paper made from it, is known as PCF (process chlorine free) if no chlorine-containing compounds were used in the recycling process. Greenhouse gas emissions Studies on paper and cardboard production estimate the emissions of recycling paper to be 0.2 to 1.5 kg CO₂-equivalent/kg material. This is about 70% of the CO₂ emissions connected with production of virgin material. Recycling statistics In the mid-19th century, there was an increased demand for books and writing material. Up to that time, paper manufacturers had used discarded linen rags for paper, but supply could not keep up with the increased demand. Books were bought at auctions for the purpose of recycling fiber content into new paper, at least in the United Kingdom, by the beginning of the 19th century. Internationally, about half of all recovered paper comes from converting losses (pre-consumer recycling), such as shavings and unsold periodicals; approximately one third comes from household or post-consumer waste. Some statistics on paper consumption: 1996: it was estimated that 95% of business information is still stored on paper. 2006: recycling of paper saves 17 mature trees, of water, of landfill space, 2 barrels of oil (), and of electricity – enough energy to power the average American home for six months. 1993: although paper is traditionally identified with reading and writing, communications has now been replaced by packaging as the single largest category of paper use at 41% of all paper used. no date: 115 billion sheets of paper are used annually for personal computers. The average web user prints 16 pages daily. 1997: on that year, 299,044 metric tons of paper was produced (including paperboard). 1999: on that year, in the United States, the average consumption of paper per person was approximately 354 kilograms. This would be the same consumption for 6 people in Asia or 30 people in Africa. 2006–2007: Australia 5.5 million tons of paper and cardboard was