Industrial areas rainwater

The atmospheric corrosion data in Table 4.34 (and also Table 13.8) is related to historic environments. Current use in the industrial areas listed with acidic pollution would show much lower corrosion rates as the corrosion of zinc in the atmosphere is essentially related to the SOj content (and the time of wetness) and in many countries the sulphurous pollution has been greatly reduced in the past 20 years. Zinc also benefits from rainwater washing to remove corrosive poultices thus, although initial corrosion rates are usually not very different on upper and lower surfaces, the latter tend —with time—to become encrusted with corrosion products and deposits and these are not always protective. 

The concentration of fluoride in rainwater is negligible. Samples of rainwater taken in eight catchments in the heavily industrialized area of Northern Europe revealed median concentrations over 30 days of less than 0.05 mg/L of fluoride [32]. 

I of rainwater in many industrialized areas of the world has increased by a factor of over 100, to a pH between 3 and 3.5. 

Wet-period rainwater samples (washout and rainout) were collected from three sites in the Hamilton area near the industrial area (beach strip), in the city centre and at the rural Hamilton Airport (Figure 1). 

It is apparent that Petaling Jaya, Perai and Senai consistently recorded the lowest pH values. The high acidity could be due to a high density of motor vehicles and industries that emit SO2 and NOx in these areas. Mersing in eastern Johore and Malacca also recorded relatively low pH values especially in later years, due to the expansion of industrial activity in these areas, and the transport of pollutants from other industrial areas. Central and eastern parts of Malaysia recorded relatively high pH values, due to the low level of industrial activity in these areas. At all stations, there was a decrease in rainwater pH between 1985 and 1988. The situation seems to... 

Relatively speaking, the concentration of contaminants in dew is higher than in rainwater, which leads to lower pH values. Heavily industrialized areas have reported pH values of dew in the range of 3 or lower. 

Traces of dissolved copper will usually be found in rainwater running off of copper-bearing surfaces. This takes place predominately in urban and industrial areas that are highly polluted with SO,. Such rainwater can cause blue staining on masonry, stonework, etc. 

This type of reaction occurs when rainwater reacts with nonmetal oxide pollutants in the air to form what has been commonly referred to as acid rain. Acid rain has been a troublesome phenomenon in regions surrounding heavily industrialized areas. Vegetation can be killed metal and granite statues are corroded and the health of people can be adversely affected by acid rain. 

That fallout of trace elements from atmospheric pollution is widespread and far from confined to urban and industrial areas, is also borne out by data published by the UK Atomic Energy Authority, who determined, by neutron activation analysis, about 30 trace elements in airborne dust, rainwater and dry deposition, sampled at regular intervals in north-west England [188]. The highest concentrations measured in air were for chlorine, sodium, calcium, aluminium, iron, lead and zinc, and there were also measurable levels of antimony, arsenic and mercury, usually in the winter months, when there was a general increase in trace-element concentration. Further data were published on the atmospheric content and total deposition of a wide range of trace elements at seven non-urban sites (one in Shetland) in the UK in the years 1972 and 1973 [189]. Data have also been published for the North Sea and the Firth of Clyde [190]. 

As mentioned in the previous section, the increased number of nuclei in polluted urban atmospheres can cause dense persistent fogs due to the many small droplets formed. Fog formation is very dependent on humidity and, in some situations, humidity is increased by release of moisture from industrial processes. Low atmospheric moisture content can also occur, especicilly in urban areas two causes are lack of vegetation and rapid runoff of rainwater through storm sewers. Also, slightly higher temperatures in urban areas lower the relative humidity. 

The atmosphere is a major source of soil acidity. Even in unpolluted environments rainwater is slightly acidic, having a pH of about 5.7 due to the dissolution of atmospheric CO2 to form the weak carbonic acid (see Worked example 5.4). The CO2 concentration in the partially enclosed soil pore system can be significantly higher (typically up to about 10 times) than in the free atmosphere due to respiration of soil microorganisms and plant roots. This results in a lower pH. In areas affected by industrial pollution, sulfur dioxide and nitrogen oxides dissolve in rainwater to produce sulfuric and nitric acids (acid rain), which are both strong acids and cause even more acidity. 

Due to heavy rainfall, wastewater overflows from sewers or industrial facilities may result in underperformance versus WQS. Nevertheless, affected sewer systems, typically combined sewer overflow (CSO) or municipal separate storm sewer systems (MS4), remain subject to NPDES regulations. CSO systems, found in older residential or muiucipal areas, allow transportation of both rainwater and raw sewage within a common stream MS4 systems separate the two flows. 

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