Dew Formation and Chemistry Near a Motorway in Poland

In this study, the influence of traffic intensity on dew formation efficiency and chemistry is presented. The measurements were conducted near the A4 motorway in SW Poland in almost flat land relief with intense agricultural activity. The dew/hoarfrost was collected by means of insulated plain passive radiative condensers at three sites: AN and AS located in the close vicinity of the motorway (30 m) on the opposite sides of the road, and AR, representing rural background conditions beyond the motorway influence. Measurements were conducted in two short campaigns in April and September 2009 with 9 and 10 collection days respectively. The average daily efficiency of dew formation was 0.179 L/m2. Its value for AN, AS and AR was on average 0.170, 0.199 and 0.173 L/m2, respectively. The efficiency of dew formation at measurement sites located on both sides of the road differed by up to about 200% during an individual dew episode. Maximum daily value reached 0.389 L/m2. The average volume–weighted pH was acidic and ranged from 4.29 (AS) to 4.58 (AR). The electric conductivity (EC) at all measurement sites was relatively low reaching on average 55.9 μS/cm for AN, 62.2 μS/cm for AS and 35.8 μS/cm for AR. The average volume–weighted TIC parameter (total ionic content) reached the value of 0.62 meq/L (AN and AS) and 0.38 meq/L (AR). Both EC and TIC values indicated strong influence of the motorway at sites located in its close vicinity (AN and AS). Depending on airflow direction during individual dew collection events, AN or AS sites were situated alternatively on windward or leeward side of the road, which distinctly influenced dew formation and chemistry: the leeward condenser was characterized by smaller water volume, higher EC and higher TIC when compared both with its windward counterpart and the background site. The ionic structure of the collected samples was similar at all measurement sites. The largest share had NO3 − anion (28–32%) and Ca2+ cation (22–25%). Thus, air pollution was relatively low in the vicinity of the A4 motorway in SW Poland not exceeding the typical values for urban background stations.