Fig. 2.

The mass spectra (left), time series (middle), and diurnal patterns (right) of five OA factors determined on the basis of PMF analysis of an HR-ToF-AMS dataset acquired in summer 2009 in New York, NY, USA. (a) LV-OOA, surrogate for regional, highly aged, low-volatility SOA; (b) SV-OOA, surrogate for less photochemically aged, semi-volatile SOA; (c) NOA, a nitrogen-enriched OA, probably derived from an SOA formed via acid–base chemistry or photochemical reactions of amino compounds, but possibly also by other mechanisms or by involvement of other reduced nitrogen compounds; (d) COA, a POA component probably dominated by cooking emissions; and (e) HOA, a surrogate for urban, combustion-related POA. In the time series plots, the corresponding time trends of tracer compounds are: (a) sulfate representing low volatility secondary aerosol species formed on regional scale; (b) nitrate and chloride representing semivolatile secondary species; (c) C₃H₈N⁺ as a tracer ion for reduced nitrogen compounds; (d) C₆H₁₀O⁺ as a tracer ion for cooking aerosols; and (e) elemental carbon and NO_x as tracer species for combustion emissions. In the HRMS of OA factors, each peak is colored on the basis of the contributions of five ion categories: C_xH_y ⁺, H_yO₁ ⁺, C_xH_yO_z ⁺, C_xH_yN_p ⁺, and C_xH_yO_zN_p ⁺. The elemental and organic mass-to-carbon ratios for each factor are shown in the legends. (Adapted from Ref. [39]) A summary of the key diagnostic plots of the PMF results is shown in Fig. 5