Laboratory studies of H sub(2)SO sub(4)/H sub(2)O binary homogeneous nucleation from the SO sub(2)+OH reaction: evaluation of the experimental setup and preliminary results

We have developed a new laboratory nucleation setup to study binary homogeneous nucleation (BHN) of sulphuric acid and water (H sub(2)SO sub(4)/H sub(2) O). Here we provide a detailed evaluation of this new experimental setup and also discuss our preliminary results by comparing with other laboratory studies. H sub(2)SO sub(4) is produced from the SO sub(2)+OH arrow right HSO sub(3) reaction and OH radicals are produced from water vapor UV absorption. The residual H sub(2)SO sub(4) concentrations ([H sub(2)SO sub(4)]) are measured at the end of the fast flow nucleation reactor with a chemical ionization mass spectrometer. The measured BHN rates (J) ranged from 0.02 and 550 cm super(− 3) s super(− 1) at the residual [H sub(2)SO sub(4)] from 10 super(8) to 10 super(10) cm super(− 3), a temperature of 288 K and relative humidity (RH) from 6 to 23%; J increased with increasing [H sub(2)SO sub(4)] and RH. J also showed a power dependence on [H sub(2)SO sub(4)] with the exponential power of 3 to 8. These results are consistent with other laboratory studies under similar [H sub(2)SO sub(4)] and RH, but different from atmospheric field observations which showed that particle number concentrations are often linearly dependent on [H sub(2)SO sub(4)]. Both particle sizes and number concentrations increased with increasing [H sub(2)SO sub(4)], RH, and nucleation time, consistent with the predictions from nucleation theories. Particle growth rates were estimated between 28 to 127 nm h super(− 1), much higher than those seen from atmospheric field observations, because of the higher [H sub(2)SO sub(4)] used in our study. While these experimental results demonstrate a validation of our laboratory setup, there are also technical difficulties associated with nucleation studies, including wall loss and H sub(2)SO sub(4) measurements.