Atmospheric aerosols are solid and liquid particles suspended in the air. Primary sources emit particles directly to the atmosphere, while secondary aerosol forms in the atmosphere. Secondary organic aerosols (SOA) from aromatic precursors are poorly constrained and their magnitude is highly uncertain. My thesis focuses on developing methods to quantify SOA in urban environments. The outcome of these analyses provide much needed insight to the abundance, composition, and variability of SOA in atmospheric particles.