Spain's CO2 emissions from fossil fuel combustion dropped 12.6 percent to 224 million tonnes in 2011, preliminary figures released on Wednesday by the EU's statistics agency Eurostat show.
Only Cyprus (down 14.7 percent) and Romania (down 14.6 percent) registered greater falls.
Eurostat found that while emissions of the gas — a major contributor to global warming — were down 2.5 percent across the 28-member bloc in 2013, they actually climbed in six countries.
The EU produced 3.35 billion tonnes of CO2 in 2013, down from the previous year's total of 3.43 billion tonnes.
Germany, Britain, France, Italy, Poland, Spain and the Netherlands account for 77 percent of the EU's CO2 emissions.
The Eurostat figures — possibly related to Spain's falling industrial production during the crisis — came on the same day that the World Health Organization issued a stark warning on the health risks of air pollution.
The WHO’s new urban air quality database covers 1,600 cities in 91 countries and shows only 12 percent of people lived in cities where air pollution levels met recommended levels.
About half of the urban population being monitored is exposed to air pollution that is at least 2.5 times higher than the levels WHO recommends — putting those people at additional risk of serious, long-term health problems.
The WHO database looked at levels of both PM10 and the more dangerous PM2.5 particles.
PM2.5 — a tiny particle under 2.5 microns, or 2.5 millionths of a metre across — is so small that it can lodge deep in the lungs, potentially causing lung and heart problems.
The recommended WHO limit for PM2.5 particles is an annual average 10 micrograms per cubic metre.
The WHO database shows the cleanest city air in Spain in 2011 was in Las Palmas on the Spanish Island of Gran Canaria with an annual average of 6 micrograms per cubic metre.
The dirtiest air was registered in the port city of La Línea de la Concepción on the south coast with an annual average of 33 micrograms per cubic metre.
The PM2.5 levels in Barcelona were 16 micrograms per cubic metre, while they the figure was 11 micrograms per cublic metre in Madrid.
The risk of early death rises by seven percent with every increase of five micrograms of PM2.5 per cubic metre, a 2013 Lancet study found.