Characteristics of size distributions at urban and rural locations in New York

Abstract

Abstract. Paired nano- and long-tube Scanning Mobility Particle Sizer (SMPS) systems were operated for four different intensive field campaigns in New York State. Two of these campaigns were at Queens College in New York City, during the summer of 2001 and the winter of 2004. The other field campaigns were at rural sites in New York State. The data with the computed diffusion loss corrections for the sampling lines and the SMPS instruments were examined and the combined SMPS data sets for each campaign were obtained. The diffusion corrections significantly affect total number concentrations, and in New York City, affect the mode structure of the size distributions. The relationship between merged and integrated SMPS total number concentrations with the diffusion loss corrections and the CPC number concentrations yield statistically significant increases (closer to 1) in the slope and correlation coefficient compared to the uncorrected values. The measurements are compared to PM2.5 mass concentrations and ion balance indications of aerosol acidity. Analysis of particle growth rate in comparison to other observations can classify the events and illustrate that urban and rural new particle formation and growth are the result of different causes. Periods of low observed PM2.5 mass, high number concentration, and low median diameter due to small fresh particles are associated with primary emissions for the urban sites; and with particle nucleation and growth for the rural sites. The observations of high PM2.5 mass, lower number concentrations, and higher median diameter are mainly due to an enhancement of photochemical reactions leading to condensation processes in relatively aged air. There are statistically different values for the condensation sink (CS) between urban and rural areas. While there is good association (r2>0.5) between the condensation sink (CS) in the range of 8.35–283.9 nm and PM2.5 mass in the urban areas, there is no discernable association in the rural areas. The average values computed for the CS lie in the range 8.7×10−3–3.5×10−2 s−1.