Abstract. In this work, we have used scanning mobility particle sizer (SMPS) and quartz crystal microbalance (QCM) to estimate the effective density of aerosol particles. This approach is tested for aerosolized particles generated from the solution of standard materials of known density, i.e. ammonium sulfate (AS), ammonium nitrate (AN) and sodium chloride (SC), and also applied for ambient measurement in New Delhi. We also discuss uncertainty involved in the measurement. In this method, dried particles are introduced in to a differential mobility analyzer (DMA), where size segregation was done based on particle electrical mobility. At the downstream of DMA, the aerosol stream is subdivided into two parts. One is sent to a condensation particle counter (CPC) to measure particle number concentration, whereas other one is sent to QCM to measure the particle mass concentration simultaneously. Based on particle volume derived from size distribution data of SMPS and mass concentration data obtained from QCM, the mean effective density (ρeff) with uncertainty of inorganic salt particles (for particle count mean diameter (CMD) over a size range 10 to 478 nm), i.e. AS, SC and AN is estimated to be 1.76 ± 0.24, 2.08 ± 0.19 and 1.69 ± 0.28 g cm−3, which are comparable with the material density (ρ) values, 1.77, 2.17 and 1.72 g cm−3, respectively. Among individual uncertainty components, repeatability of particle mass obtained by QCM, QCM crystal frequency, CPC counting efficiency, and equivalence of CPC and QCM derived volume are the major contributors to the expanded uncertainty (at k = 2) in comparison to other components, e.g. diffusion correction, charge correction, etc. Effective density for ambient particles at the beginning of winter period in New Delhi is measured to be 1.28 ± 0.12 g cm−3. It was found that in general, mid-day effective density of ambient aerosols increases with increase in CMD of particle size measurement but particle photochemistry is an important factor to govern this trend. It is further observed that the CMD has good correlation with O3, SO2 and ambient RH, suggesting that possibly sulfate secondary materials have substantial contribution in particle effective density. This approach can be useful for real-time measurement of effective density of both laboratory generated and ambient aerosol particles, which is very important for studying the physico-chemical property of particles.
Long-term measurement of PM2.5 mass concentration using an electrostatic particle concentrator-based quartz crystal microbalance integrated with carbon dioxide aerosol jets for PM sensing in remote areas
