Chemical mass closure and spatial and seasonal characteristics of coarse particulate matter in the Los Angeles area

Minerals and trace elements comprise a major fraction of CPM mass, with annual mass fractions vary from 41.2%-60.5% across the 10 sampling sites. Inorganic ions and organic matter also contributed substantially, with an average ratio of 22.6% and 19.7%, respectively. In particular, nitrate was the most abundant specie in CPM, with an average mass fraction of about 17.2%. Sea salt concentration, estimated using Cf concentration and the corresponding sea salt fraction of Na⁺, Mg²⁺, K⁺, Ca ²⁺, SO₄^2-, was also a significant portion of CPM with an average mass fraction of 9.14%). Organic carbon was well correlated with minerals and trace elements. Particularly, higher correlation coefficients were found with soil dust tracers (R = 0.74 and 0.72 for Ti and Fe, respectively), suggesting that semi-volatile organic compounds and/or biological materials might play a significant role in particulate OC of the coarse mode.