Bulgaria's Air Is Dirtiest in Europe, Study Finds, Followed by Poland Dimitar Dilkoff/Agence France-Presse - Getty Images Smokestacks last February in Sofia, Bulgaria. A European study found that Bulgaria had the highest levels of two kinds of particulate matter that can lead to health problems from asthma to cancer. Hold your breath if you visit Bulgaria. The air in the small Black Sea nation is thicker with several major air pollutants than the air in any other country in Europe, according to a new study prepared by Europe's environmental regulators. Bulgaria has the highest concentrations of the two major varieties of particulate matter, which are tiny airborne droplets or gas particles that come from smokestacks, vehicle tailpipes or a variety of other sources. They can lead to health problems from asthma to cancer. Bulgaria also has the highest concentrations of carbon monoxide and sulfur dioxide, according to the report by the European Environment Agency. The pollution in Bulgaria's capital of Sofia is evident to anyone who has spent any time there. "When you put on a washed white shirt and take a walk for a couple of hours in Sofia, when you come back you can see that the collar and the front have a yellow-gray hue," said Alex Melamed, a 25-year-old business student who lives in the city of about 1.2 million people. Sometimes I do the following experiment: I walk around in Sofia and do not touch anything, when I come back and wash my hands, the soap gets dirty. But Bulgaria is hardly alone in having air quality challenges. While Bulgarian cities lead in the concentration of particulates, Poland is a frequent runner-up, and cities in northern Italy lead in ozone, according to separate data provided by the agency. Over all, in the 10 years measured by the report - from 2002 to 2011 - air pollutants are generally on the decline in Europe. But particulates and ozone remain a problem. An increase in the percentage of urban populations in Europe being exposed to levels of particulate matter from 2010 to 2011 suggested some backsliding, the report said. The development was attributed to dry spells in the period, which slow the dispersal of particulates. But it also could reveal a growing reliance on wood burning for home heating in some countries during the financial crisis, the agency said. "Large parts of the population do not live in a healthy environment," Hans Bruyninckx, the executive director of the European Environment Agency said in a statement. To get on to a sustainable path, Europe will have to be ambitious and go beyond current legislation. Bulgaria has a history of Soviet-era industrialization with scant attention paid to environmental issues. Given its standing as one of Europe's poorer nations, it appears to have made limited progress in cleaning up its air. A 2011 report from the United Nations found that Bulgaria, along with Armenia and Romania, "lead the world in deaths from outdoor air pollution." That said, the particulate levels reported in Bulgaria fall well short of the alarming levels reported recently in Beijing, where in January the concentration of fine particulate matter reached 40 times the exposure limit recommended by the World Health Organization. Four of Europe's five cities with the most consistently high levels of particulate matter were Bulgarian, with Pernik, a small city just southwest of the capital, Sofia, at the top of the list. High concentrations of particulates were found in the air in Pernik about half of the year, compared to about 15 days of the year for Paris and Stuttgart, Germany. Part of the problem in Bulgaria and its neighbors has been the use of wood for home heating. "Populations are switching to domestic fuels when they can't afford energy prices," said Valentin Foltescu, an air quality expert at the agency. Poland, where coal-burning predominates, also ranks at or near the bottom of several air quality measures. It had the highest levels of benzo (a) pyrene, a carcinogen that comes from coke and steel production as well as from fuel. Bulgaria and the Czech Republic also had high levels of benzo (a) pyrene. But another former Soviet bloc nation, Estonia, frequently had the cleanest air. Air quality problems, of course, are hardly constrained within borders, and some of it has to do with which way the wind blows. Less than half of the fine particular matter seen in many European countries actually results from emissions within the country's own borders, the report found. Europe's efforts to reduce ozone emissions are undercut by the movement of ozone across continental borders. Italy's ozone problem is considered to be a combination of weather and industry. In northern Italy's Po Valley, Mr. Foltescu said, "you have the industrial activity, you have the trapping of pollution, you have the high temperatures. You have all the ingredients to promote high levels of ozone. The study examined air quality broadly in Europe, and included data from beyond the European Union, though not all of the 38 countries that participated provided a full range of data. "Surveys show that a large majority of citizens understand well the impact of air quality on health and are asking public authorities to take action at E.U., national and local levels, even in times of austerity and hardship," Janez Potocnik, Europe's commissioner of the environment, said in a statement. Georgi Kantchev contributed reporting.