## 1 Introduction  
The determination of suspended particulate mass concentrations (minerogenic mass, biomass, chlorophyll content) in marine particle populations is a matter of particular interest to ocean sciences,and one of the key aspects of the characterization of the properties of marine particles. The relationship between particulate mass properties and optical properties of seawater is important for understanding the formation of optical remote sensing signals and their interpretation.  
In previous work carried out on a set of seawater samples collected in UK coastal waters (UKCW dataset), a Mie-based flow cytometric method (FC method) was developed to determine particle size distributions (PSDs) and real refractive index distributions (PRIDs), and its results used as inputs for Mie theory forward modelling to reconstruct not only bulk inherent optical properties (IOPs), but also individual fractions and optical contributions from inorganic, organic, and fluorescent particle subpopulations [1; 2]. Although flow cytometric determination of particle physical properties and the subsequent modelling of IOPs have some precedent [3; 4; 5], no true effort has been devoted to extending the procedure to the reconstruction of particulate mass concentrations from flow cytometric data. Indeed, coupled with models of particle density and carbon intraparticle concentration, particle size, and real refractive index distributions offer the chance to explore the biogeochemical properties of a particle population from a new perspective.  
In this study, models of organic and inorganic particle density are adapted from literature and applied to the UKCW dataset to produce modelled values of suspended particulate matter (SPM), organic suspended matter (OSM), and inorganic suspended matter (ISM). Furthermore, cell volume scaling models and refractive index-based models are also adapted from literature to allow estimation of intraparticle carbon (\(C_{i}\)) and intraparticle chlorophyll-a (\(Chl_{i}\)) content, ultimately producing modelled values of particulate organic carbon (POC) and chlorophyll-a concentrations (ChlA) from the particle data of the UKCW dataset. The modelled values thus obtained are then compared against the results of actual biogeochemical measurements, and the parameters used to assess carbon and chlorophyll concentrations are optimized on a dataset-wide basis to explore the physiology of the cells encountered during the He442 research cruise. A summary of the abbreviations and notations used throughout the study is given in Table 1.  
\begin{table}
\begin{tabular}{l l} \hline \hline
**Notation** & **Definition** \\ \hline ChlA & Chlorophyll-a concentration, mg m\({}^{-3}\) \\ FC & Flow cytometer; flow cytometry \\ IOP & Inherent optical property \\ ISM & Inorganic suspended matter, g m\({}^{-3}\) \\ OSM & Organic suspended matter, g m\({}^{-3}\) \\ SPM & Suspended particulate matter, g m\({}^{-3}\) \\ POC & Particulate organic carbon, mg m\({}^{-3}\) \\ PRID & Particle real refractive index distribution \\ PSD & Particle size distribution \\ RMS\%E & Root-mean-square percentage error \\ RMSE & Root-mean-square error \\ UKCW & UK coastal waters (dataset) \\ \(a\), \(a_{C}\), \(a_{chl}\) & Slopes of the refractive index-based models and of the of the \(C_{i}\) and \(Chl_{i}\) optimized \\ \(b\) & \(y\)-intercepts of the refractive index-based models, kg m\({}^{-3}\) \\ \(F(r)\) & Fractal dimension, dimensionless \\ \(h_{1}\), \(h_{2}\) & Power law exponents of the optimized POC and ChlA volume scaling functions \\ \(k\) & Particle size distribution scaling coefficient, mL\({}^{-1}\) \\ \(k_{1}\), \(k_{2}\) & Scaling coefficients of the optimized POC and ChlA volume scaling functions respectively, \\ \(m_{tot}\) & Total particle mass, mg \\ \(C_{i}\) & Intraparticle carbon concentration, kg m\({}^{-3}\) \\ \(Chl_{i}\) & Intraparticle chlorophyll-a concentration, kg m\({}^{-3}\) \\ \hline \hline \end{tabular}
\end{table}
Table 1: Abbreviations and notations used in this study.