On the time-averaging of ultrafine particle number size spectra in vehicular plumes X. H. Yao1, N. T. Lau1, M. Fang1, and C. K. Chan2 1Institute for the Environment, Hong Kong University of Science and Technology, Clear Water Bay, Hong Kong, People's Republic of China 2Department of Chemical Engineering, Hong Kong University of Science and Technology, Clear Water Bay, Hong Kong, People's Republic of China
Abstract. Ultrafine vehicular particle (<100 nm) number size distributions presented in the
literature are mostly averages of long scan-time (~30 s or more)
spectra mainly due to the non-availability of commercial instruments that
can measure particle distributions in the <10 nm to 100 nm range faster than 30 s even though individual researchers have
built faster (1–2.5 s) scanning instruments. With the introduction of the
Engine Exhaust Particle Sizer (EEPS) in 2004, high time-resolution (1 full
32-channel spectrum per second) particle size distribution data become
possible and allow atmospheric researchers to study the characteristics of
ultrafine vehicular particles in rapidly and perhaps randomly varying high
concentration environments such as roadside, on-road and tunnel. In this
study, particle size distributions in these environments were found to vary
as rapidly as one second frequently. This poses the question on the generality of using
averages of long scan-time spectra for dynamic and/or mechanistic studies in
rapidly and perhaps randomly varying high concentration environments.
One-second EEPS data taken at roadside, on roads and in tunnels by a mobile
platform are time-averaged to yield 5, 10, 30 and 120 s distributions to
answer this question.
Citation: Yao, X. H., Lau, N. T., Fang, M., and Chan, C. K.: On the time-averaging of ultrafine particle number size spectra in vehicular plumes, Atmos. Chem. Phys., 6, 4801-4807, doi:10.5194/acp-6-4801-2006, 2006.