Design and performance of an automatic regenerating adsorption aerosol dryer for continuous operation at monitoring sites

Sizes of aerosol particles depend on the relative humidity of their carrier gas. Most monitoring networks require therefore that the aerosol is dried to a relative humidity below 50% r.H. to ensure comparability of measurements at different sites. Commercially available aerosol dryers are often not suitable for this purpose at remote monitoring sites. Adsorption dryers need to be regenerated frequently and maintenance-free single column Nafion dryers are not designed for high aerosol flow rates. We therefore developed an automatic regenerating adsorption aerosol dryer with a design flow rate of 1 m3/h. Particle transmission efficiency of this dryer has been determined during a 3 week experiment. The lower 50% cut-off was found to be smaller than 3 nm at the design flow rate of the instrument. Measured transmission efficiencies are in good agreement with theoretical calculations. One dryer has been successfully deployed in the Amazon river basin. We present data from this monitoring site for the first 6 months of measurements (February 2008–August 2008). Apart from one unscheduled service, this dryer did not require any maintenance during this time period. The average relative humidity of the dried aerosol was 27.1+/−7.5% r.H. compared to an average ambient relative humidity of nearly 80% and temperatures around 30°C. This initial deployment demonstrated that these dryers are well suitable for continuous operation at remote monitoring sites under adverse ambient conditions

Weak correlation of ultrafine aerosol particle concentrations <800nm between two sites within one city.

Ambient aerosol has been identified as a major pollutant affecting human health. Standards to reduce particles mass concentrations have therefore been established in many countries. Recent studies suggest that the number concentration of aerosol particles, which is dominated by the ultrafine size range smaller than 100 nm in diameter, may be independently associated with health effects. Currently, epidemiological evidence for such effects is conflicting. We have measured aerosol size distributions at two stations (urban background, street canyon) located at a distance of 1.5 km for a time period of 1 year. Number concentrations and particle size distributions at both sites were significantly different. Short-term correlation between the two sites was weak for individual measurements of number concentrations and size bins of ultrafine particles (0.19-0.46). Correlation coefficients for hourly and daily averages in selected size ranges ranged from 0.35 to 0.46. On the other hand, the correlation coefficient for daily average particle volume concentrations was found to be 0.67. About 10% to 20% of the population of European cities lives close to roads with traffic densities comparable to our site. The underestimation of the exposure of a considerable part of a study population may therefore severely influence the outcome of epidemiological studies focused on health effects associated with ultrafine particles. A single background measurement site may not be sufficient for exposure assessment in these studies without taking spatial and temporal variability into account

Long-term measurements of size-segregated ambient aerosol in two German cities located 100km apart.

Epidemiological studies suggest that exposure to sub-micrometer aerosol particles poses a health risk. In this study, we had the unique opportunity to investigate the comparability of the ambient aerosol measured at urban background stations in two cities located in one region. We compared particle number size distributions measured in Erfurt and Leipzig, Germany, over a 5-year period from February 1997 through August 2001. Our findings show that mean concentrations, size distributions and their diurnal variations of the ambient aerosol measured at urban background stations in two cities are very similar. Total particle number concentrations (10–800 nm) measured in Erfurt were only 9–20% higher compared to those measured in Leipzig. Average number concentrations in the size ranges 10–20, 20–50, 50–100, 100–200, and 200–800 nm differed by less than 50%. Diurnal variations in particle number distribution in summer and winter in Erfurt showed similar patterns to those in Leipzig. Evidence that the site in Erfurt was more influenced by local traffic compared to the site in Leipzig is the shifts in size distribution towards larger particles in Leipzig along with the 37–43% higher concentration of particles smaller than 30 nm in diameter and the two to three times elevated NO concentrations in Erfurt on workdays. Observed differences between Erfurt and Leipzig size distributions can be attributed to differences in horizontal distance to major roads, inlet heights, terrain, and climatic conditions. Our results suggest that the average urban background aerosol in two cities in the same region is similar if the major sources of the aerosol (traffic, domestic heating) in these two cities are similar