Sources to formic acid studied by carbon isotopic analysis and air mass characterization

The carbon isotopic composition of formic acid samples from a rural and a s emi-remote area in Denmark has been investigated by collection of 5-6 day i ntegrated samples during winter and spring. The results show that 80-100% o f formic acid stems from biogenic VOC emitted from terrestrial sources. Eve n during winter there is a dominating biogenic contribution, which is surpr ising since biogenic emissions are very low at these latitudes in that peri od. Quality assurance samples have been used to check the reliability of the co llection and pre-treatment procedures for atmospheric formic acid samples. The carbon isotopic investigation was supplemented by measurements of benze ne, toluene, formaldehyde, acetone, acetaldehyde and nitrogen dioxide in or der to characterise the air masses of one formic acid sample. The general a ir mass analysis showed that the sampling site, a semi-remote area, was wit hout significant local air pollution sources. During the formic acid sampli ng period, the air masses were influenced by both direct anthropogenic emis sions (benzene, toluene, nitrogen dioxide and acetone) and compounds formed during long-range transport of anthropogenic hydrocarbons (formaldehyde an d acetaldehyde). Nevertheless, formic acid still had a predominantly (89 +/ - 5%) biogenic origin. (C) 2000 Elsevier Science Ltd. All rights reserved.