Development of a variable-path-length diffusive sampler for ammonia and evaluation of ammonia pollution in the urban area of Rome, Italy

A variable-path-length diffusive sampler for the determination of atmospheric ammonia was developed and tested. Polyethylene was found to be the best material for the construction of the sampler, while a glass body sampler of similar design yielded unreliable results; phosphorous acid was the best collecting medium. The low level of the field blanks and the high operative capacity make this device able to operate in a very wide loading range (0.3–100 μg); the possibility to vary the length of the diffusive pathway allows a further increase of the detectable concentration range (0.1–125 μg m−3 during a 1-month exposure). Reproducibility is better than 5% and the comparison with reference denuders demonstrated a good accuracy of the method (deviation lower than 5%). The deployment of these samplers in some field campaigns carried out in Rome allowed us to confirm the close link between ammonia concentration and traffic emission and to get an insight into the spatial variability of this pollutant.