The pressurised metered dose inhaler (pMDI) is the most widely prescribed device for asthma treatment and COPDs. The pMDI products of the industrial collaborators in this work (Chiesi Farmaceutici SpA) are solution formulations of HFA propellants and ethanol co-solvent to solubilise the active pharmaceutical ingredient. This paper reports the findings of a PDA study of aerosol plumes generated by a commercial actuator (Bespak 630 series). The work establishes a methodology to determine number of, and time delay between, actuations required to obtain robust values of event-averaged spray velocity and droplet size metrics. The presented findings used relevant formulations containing HFA134a propellant with ethanol (up to 20 % w/w). The method uncertainty was defined as the difference between values of event-averaged velocity and drop sizes D10 and SMD after N-1 and N actuations. The minimum number of actuations to obtain an uncertainty of ± 1 % for these spray metrics was found to be 30 using a delay between successive actuations of 1 minute. This paper presents data for the temporal variation of aerosol velocity and droplet size at 15 mm from the spray orifice exit for varying formulation, independent of geometric variables. With ethanol concentration varying from 0 to 20 % w/w, the duration of the spray event was found to reduce from 297 to 195 ms, the plume velocity remained broadly constant at 40.6 ± 2.6 m.s-1, but SMD droplet size reduced from 8.83 to 6.15 μm. However, drop size trends show non-linear behaviour with increasing ethanol concentration. Previous studies have suggested that the aerosol velocity and particle size are strongly linked with the formulation vapour pressure, which is controlled by the ethanol concentration. The current study demonstrates a minimal link between ethanol concentration and vapour pressure and, hence, aerosol velocity, but shows a link between ethanol concentration and droplet size, suggesting that other physical properties (e.g. surface tension and/or viscosity) play more significant roles in governing the drop size than previously acknowledged.