Frank Griessbaum

Direct measurement of CO2 and particle emissions from an urban area

From July 9 th through September 24th, 2009, turbulent particle number fluxes and CO 2 fluxes were measured above the city area of Munster, north-west Germany. The goal was to characterize the respective vertical fluxes in the urban boundary area. The measurements were conducted at a height of 65 m a.g.l. on a military radio tower at 10 Hz temporal resolution. Fluxes were calculated applying the eddy covariance method. To determine the impact of traffic emissions on particle number fluxes and CO 2 fluxes, hourly traffic activities for 45° sectors, related to the tower, were calculated. Averaged diurnal and sectoral fluxes are consistently directed upward, implying that the urban area of Munster acts continuously as particle (number) and CO 2 source. Traffic activities vary in the course of the day and within the 45° sectors. The latter is attributable to differences in land use between the sectors. In the course of the day, two peaks are discernible, during the morning and the evening rush hours, respectively. Averaged diurnal particle (number) fluxes are correlated significantly to traffic activity. Accordingly, traffic related emissions are the main sources for urban particle (number) fluxes. Averaged sectoral CO 2 fluxes also correlate fairly well with sectoral traffic activities. In addition, daytime photosynthesis is a controlling variable for the CO 2 flux, leading to lower upward fluxes in daytime. The contribution of the photosynthetic activity of the vegetation in the urban area to the CO 2 flux is quantified. Further, the contribution of traffic related emissions to the CO 2 flux is computed by applying emission factors for carbon dioxide to the traffic activity. They contribute in daytime about 40 to 50 % to the CO 2 flux, whereby, nightly contributions are minimal.

One-year measurement of size-resolved particle fluxes in an urban area

Size-resolved particle flux measurements were carried out in an urban area from April 2012 to April 2013. Together with a standard eddy covariance system, two fast optical particle counters have been employed on a 65-meter-high tower in Münster, Germany. Particle number fluxes were directly calculated for particles with diameters from 0.06 to 10 µm within 16 individual size-bins. Whereas particle number concentrations show a distinct yearly pattern with maxima in winter and minima in summer, the flux time series is more multifaceted. Average daily maxima of 3.0e+07 particles m−2 s−1 occurred during winter while minima of 2.0e+06 particles m−2 s−1 were observed in fall. The size-resolved measurements revealed that during spring and summer a considerable number of accumulation mode particles deposits while a simultaneous net particle emission occurred, which is mostly driven by particles smaller than 0.12 µm. These bi-directional fluxes lead to a net mass deposition of up to 13.5 µg m−2 d−1. The tipping-point between the emission and deposition lay between 0.16 and 0.19 µm. In a comprehensive analysis of the flux and concentration time series, the degree of atmospheric stability, the seasons, and the type of source region have been identified as key influences for particle fluxes. Different responses between particle fluxes and concentrations have been found along these drivers.

Size-resolved flux measurement of sub-micrometer particles over an urban area

From April 11 th to May 27 th , 2011, the turbulent exchange of sub-micrometer particles between the urban surface and the urban boundary-layer was measured above the city area of Munster (NW Germany). The scope of the study is to examine the contributions of particles of different size classes to the total measured fluxes. Eddy-covariance measurements were performed at 65 m above ground. The particle concentrations in 99 size bins with particle diameters ranging from 55 to 1000 nm were measured with an optical particle spectrometer. For flux calculations we grouped these 99 original bins into 18 wider channels with an upper cut-off of 320 nm, and a further rather coarse channel for particles up to 1 lm. The overall results reveal that Munster is a relevant source of about 2.8 AE 10 8 particles m � 2 d � 1 on weekdays and 1.8 AE 10 8 particles m � 2 d � 1 on Sundays within the indicated size range. These emissions are predominantly driven by secondary particles of the Aitken mode, which are most likely caused by traffic. Hence traffic hotspots are a major contribution to the net fluxes. On the other hand, considering the mass fluxes, Munster is a sink of 0.53 l gm � 2 d � 1 on weekdays and 0.08 l gm � 2 d � 1 on Sundays. Here, mainly particles of the accumulation mode with diameters above 167 nm lead to deposition fluxes. Number and mass fluxes exhibit distinct daily and weekly patterns.

A Collector for Fog Water and Interstitial Aerosol

Abstract An active heatable cloud water collector for ground sampling is presented. The collector can be operated unattended for approximately one week, even in harsh winter conditions. The collection strands are Teflon tubes. A preset cycle of 15-min sampling followed by 250 s of mild heating using wires inserted into the tubes is used. The lower cutoff diameter for fog droplets is 7.3 μm, and its overall collection efficiency is 79% for the liquid water content of fogs at the experimental site in central Europe. It performed reliably during a 2-yr experiment. The collected fog water interacts exclusively with inert materials such as Teflon and Perspex so the collector is well suited for trace analyses of fog water. The collector can be upgraded with an interstitial aerosol collection unit, at the expense of unattended operation. The lower cutoff diameter of the fog water collection strands is 8.1 μm when the interstitial aerosol module is installed. The module efficiently collects particles with diamete...

Canopy‐atmosphere interactions under foggy condition—Size‐resolved fog droplet fluxes and their implications

Microphysical processes of fog and their spatial and temporal pattern are a challenge to study under natural conditions. This work focuses on the development of bidirectional fluxes of fog droplets above a forest canopy in northeastern Taiwan. Bidirectional fluxes occurred regularly, start from the smallest droplet class (<2.66 µm diameter), and subsequently extend to larger droplets up to 7.41 µm diameter. The development of the bidirectional fluxes with positive (upward) fluxes of smaller droplets and downward fluxes of larger fluxes is associated with a temperature gradient and with the activation of fog droplets according to the Kohler theory. Small fog droplets develop close to the canopy as result of evapotranspiration and subsequent condensation. The rapid growth of small fog droplets and the accelerated growth of activated droplets, a process which is more likely to occur at higher levels of the fog layer, lead to a sink of small droplets and a source of larger droplets within the fog. This is in accordance with the observation that positive droplet number fluxes of small fog droplets outnumber the negative fluxes from the larger fog droplets. For liquid water, the net flux is negative.