Measurement and Modeling of the Diurnal Cycling of Atmospheric PCBs and PAHs

Abstract

PCBs and PAHs were quantified in air samples taken every 6 h over a 7 day period in August 1995 at a rural site in northwest England. For the first 5 days, a stable high-pressure system moved slowly across northern England from the east. During this time, PCB air concentrations responded very closely to the changes in ambient temperature, following a clear diurnal cycle. All PCB congeners correlated well with temperature, but the correlation was strongest for lower chlorinated species. Daily PCB concentration maxima exceeded minima by a factor of 2.1-3.7 for different congeners; in contrast, daily maxima:minima ratios for different PAHs were in the range 0.47-1.44. These data are interpreted as providing evidence that rapid, temperature-controlled air-terrestrial surface exchange of PCBs influencing air concentrations and, hence, regional/global scale cycling of these compounds occurs. Toward the end of the study period, the stable air conditions were replaced by a turbulent (windy), unstable low-pressure system, when day/night temperature differences were small and the diurnal PCB congener pattern was not discernible. Diurnal PAH concentration changes were not correlated with temperature, but groups of compounds were strongly correlated with each other (e.g., phenanthrene, fluoranthene, and pyrene; benzo(k)fluoranthene, benzo(a)pyrene, benzo-(ghi)perylene). It is therefore hypothesized that short-term PAH air concentrations are controlled by ongoing recent local/regional source inputs (rather than air-surface recycling), atmospheric reactions, and deposition processes. The air-surface exchange of PCBs is satisfactorily modeled by a sine curve describing ambient temperatures and controlled by a temperature-dependent air-terrestrial surface (K TA ) partition coefficient.

The contribution of traffic to indoor concentrations of polycyclic aromatic hydrocarbons†

“…While average temperatures between the locations varied between 768 and 898F, a linear regression suggested that PAS response was unrelated to temperature for all locations (r 2 =0). This finding is supported by previous studies showing no significant trends between temperature and PAS response or PAH concentrations under normal environmental conditions Lee et al, 1998). Wilson et al (1994) also reports that PAS response was unaffected by relative humidity.…”

Short-term variation in ambient concentrations and gas/particle partitioning of organochlorine pesticides in Izmir, Turkey

“…Studies by Lee et al (2000Lee et al ( , 1998 have reported that OCPs and other SOCs followed clear diurnal cycles for the first 5 days of their study when the stable atmospheric conditions were dominant. However, for the last 2 days as a more unstable and cooler weather started to influence the sampling site, OCP concentrations were controlled primarily by advection (Lee et al, 2000).…”

“…As the temperature rises, gas-phase air concentrations increase as a result of volatilization from previously contaminated surfaces such as soil, atmospheric particles, water, and vegetation. Short-term studies have indicated that ambient gas-phase SOCs also respond to short-term temperature changes resulting in rapid movement between environmental compartments (i.e., diurnal cycling) (Lee et al, 1998(Lee et al, , 2000. Advection and ongoing sources are other important factors affecting the variation of ambient gas-phase OCP concentrations.…”

Diurnal Variability of Persistent Organic Pollutants in the Atmosphere over the Remote Southern Atlantic Ocean

“…This was the first time that such a diel cycle had been reported over the open ocean. Diel cycles had previously been observed in several studies on land (e.g., [8][9][10][11][12][13][14]); however, high daytime concentrations were usually associated with high daytime temperatures, which were not observed in the cycle over the ocean. Jaward et al [6] hypothesized that interactions between plankton and the dissolved phase may play a role in their observations, but stated that further measurement data were needed to evaluate this hypothesis.…”