Organic nitrogen in the atmosphere – where does it come from? A review of sources and methods

Abstract

This review considers the ways in which atmospheric organic nitrogen has been measured and linked to potential sources. Organic N exists in gas, particle and dissolved phases and represents a large (ca. 30%) fraction of total airborne nitrogen, but with large variability in time and space. Although some components (e.g. amines) have been the subject of several studies, little information is available for the many other components of organic N that have been identified in individual measurements. Measurements of organic N in precipitation have been made for many decades, but both sampling and chemical analytical methods have changed, resulting in data that are not directly comparable. Nevertheless, it is clear that organic N is ubiquitous and chemically complex. We discuss some of the issues which have inhibited the widespread adoption of organic N as a routine analyte in atmospheric sampling, and identify current best practice. Correlation analysis is the most widely used technique for attributing likely sources, examining the co-variation in time and/or space of organic N with other components of precipitation or particulate matter, yet the shortcomings of such simple approaches are rarely recognized. Novel measurement techniques which can identify, if not yet quantify, many of the components of particulate or dissolved organic N greatly enhance the data richness, thereby permitting powerful statistical analyses of co-variation such as factor analysis, to be employed. However, these techniques also have their limitations, and while specific questions about the origin and fate of particular components of atmospheric organic N may now be addressed, attempts to quantify and attribute the whole suite of materials that comprise atmospheric organic N to their sources is still a distant goal. Recommendations are made as to the steps that need to be taken if a consistent and systematic approach to identifying and quantifying atmospheric organic N is to progress. Only once sources have been recognised can any necessary control measures to mitigate adverse effects of atmospheric organic N on human health or ecosystem function be determined