Measurement System for Particulate Nitrate Based on the Scrubber Difference NO−O3 Chemiluminescence Method in Remote Areas

Abstract

A particulate nitrate analyzer based on a scrubber difference/NO-O3 chemiluminescence method (SD-CL method) has been developed for measuring nitrate concentrations in remote areas. Particulate nitrate concentrations (NO3(-)(p)) were analyzed by the difference between the concentrations of NOy - gaseous nitric acid (HNO3) and NOy - HNO3 - NO3(-)(p). Annular denuders coated with NaCl and PTFE filter were used as the scrubbers for HNO3 and NO3(-)(p), respectively. The transmission efficiency of coarse particles in the denuder was found to be 93.4 ± 5.8%, so the loss of NO3(-)(p) to the denuder was within the uncertainty of the particulate nitrate analyzer (±20%). The measurements of NOy, HNO3, and NO3(-)(p) were conducted from March 15 to April 31, 2008, at Cape Hedo, Okinawa, Japan. Over 99.5% of the observed concentrations of NO3(-)(p) for 10 min integration times were higher than the detection limit of the SD-CL method (0.18 μg m(-3)). The least-squares fit of the R&P nitrate monitor against the SD-CL method yielded a slope of 0.67 ± 0.02 and a correlation coefficient of R = 0.73. This result indicates that this method could also measure NO3(-)(p) when the diameter of aerosols was larger than 10 μm. The SD-CL method was found to be useful as a measurement system for NO3(-)(p) in remote areas where coarse NO3(-)(p) dominates.