Instantaneous secondary organic aerosol yields and their comparison with overall aerosol yields for aromatic and biogenic hydrocarbons

An instantaneous secondary organic aerosol yield (IAY) is a different quantity than an overall aerosol yield (OAY), both qualitatively and quantitatively. Starting from Odum's OAY equation, this paper derives and presents a new equation for the calculation of IAY values. As examples, the two-product form of the equation is applied to 10 representative aromatic and biogenic reactive organic gas (ROG) experiments in the literature. Values of IAY and OAY corresponding to wide ranges of organic aerosol mass concentrations (M-0) are calculated using the new IAY equation in this paper and the original Odum's OAY equation. These IAY and OAY values are shown through aerosol yield curves, which are the plots of IAY or OAY versus M-0. Comparative analysis of the IAY and OAY curves shows that both IAY and OAY increase monotonically with M-0 and they approach a common maximum value when M-0 becomes very high. However, when M-0 approaches zero, OAY also approaches zero but IAY approaches a fixed positive value for a given ROG. At any given M-0 value, the value of IAY is always higher than that of OAY. The relative differences between IAY and OAY are especially significant under typical ambient and experimental M-0 levels. IAY values can be orders of magnitude higher than OAY values and are much better representations of aerosol yields under these M-0 levels. When it is used for secondary organic aerosols (SOA) estimation and modelling, the new IAY equation will significantly improve the underestimation of SOA formation caused by directly using the original OAY equation. More sophisticated SOA algorithms could also be developed based on the IAY equation presented here. Crown Copyright (C) 2003 Published by Elsevier Ltd. All rights reserved.