Inorganic nitrogen (IN) and organic nitrogen (ON) molecules constitute a significant part of atmospheric aerosol. Unlike IN, the total ON quantity remains largely unquantified due to a lack of simple and direct measurement method. This analytical deficiency hinders the quantitative assessment of the various environmental and health effect impacts by aerosol ON. In this work, we developed an analyzer system that utilizes programmed thermo-evolution of carbonaceous and nitrogenous aerosols and chemiluminescent detection of nitrogen signal. Furthermore, Positive Matrix Factorization (PMF) is used as a multivariate curve resolution method to analyze carbon and nitrogen thermograms, which produces separate quantification of IN and ON. The PMF-resolved ON and IN amounts are verified of their measurement accuracy for laboratory-generated mixtures of IN and ON standards, as well as for ambient aerosol samples through comparison with independently-measured IN concentrations using ion chromatograph. The system is capable of detecting IN and ON as low as 96 ng N per sample on a small filter aliquot (1 cm²) without any pretreatment. This method breakthrough opens the door to quantifying an important pool of aerosol N that was analytically inaccessible in the past and holds the promise to quantifying IN and ON in other environmental samples. As a demonstration, quantification of aerosol ON at an urban site in Hong Kong, China in samples spanning over a year reveals ON constituting a significant fraction (9-52%) of the total aerosol nitrogen and having major source origins in both secondary formation and primary emissions.
 

Organic aerosols,nitrogenous aerosol,organic nitrogen,method development,thermal evolution