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					Greg Caseley
Pollution Monitoring Reasearch
Why Monitor Air Pollution?
Monitoring provides raw measurements of air pollutant concentrations. With appropriate
analysis and interpretation, these measurements can be transformed into useful
information on the quality of the air.

This information has many uses and the measurements can provide essential data to
help answer a wide variety of questions such as:

 How bad is air pollution?
 How does air pollution vary with time and location?
 Is air pollution getting better or worse?

How is air pollution measured?
Pollution can be measured in many ways, from simple physical and chemical
measurements, to sophisticated electronic methods. Three main methods of measuring
air pollution are used.

The methods are :

      Passive Sampling
      Active Sampling
      Automatic Sampling

Passive Sampling Methods

Diffusion tubes or badges provide a simple and inexpensive method of screening air
quality in an area, to give a general indication of average pollution concentrations over a
period of weeks or months. These are simple plastic tubes or discs, open at one end to
the atmosphere and with a chemical absorbent at the other end. They collect a sample
over a period between a week and a month which is then analysed in the laboratory. The
low cost per tube permits sampling at a number of points in the area of interest; this is
useful in highlighting “hotspots” of high concentrations, near for example major roads or
emission sources, where more detailed studies may be needed.

Active sampler methods

Sampler methods collect pollutant samples either by physical or chemical means for
subsequent analysis in a laboratory. Typically, a known volume of air is pumped through
a collector such as a filter or chemical solution for a known period of time, which is then
removed for analysis. Samples can be taken each day, thereby providing measurements
for shorter periods of time, but at a relatively low cost compared with automatic
monitoring methods. There is a long history of sampler measurements in the UK and
throughout Europe, providing valuable baseline data for trend analyses and comparison.




Automatic Methods
These produce high resolution measurements (typically hourly averages or better) at a single
point for pollutants such as ozone, oxides of nitrogen, sulphur dioxide, carbon monoxide and
particulates (PM10). Methods used include a variety of spectroscopic methods such as infra-
red or ultra-violet absorption, ultra-violet fluorescence, chemiluminescence, or for
particulates, a variety of sophistaicated filtration techniques. Gas Chromatography (GC)
analysers also provide high resolution data on benzene, 1,3-butadiene and other speciated
hydrocarbon concentrations. The sample is analysed on-line and in real-time. This is the most
expensive method of air quality monitoring routinely employed. In order to ensure that the
data produced are accurate and reliable, a high standard of maintenance, operational and
quality assurance/control procedures is often required.

The main pollutant species measured are:

           Ozone (O3)                      and 25 hydrocarbon species
           Nitrogen dioxide (NO2)      Benzene           Ethyne
           Nitric oxide (NO)           1,3-Butadiene     Isoprene
           Oxides of nitrogen          iso-Butane        Methyl pentane
            (NOx)                       n-Butane          iso-Pentane
           Carbon monoxide (CO)        trans-2-Butane    n-Pentane
           Sulphur dioxide (SO2)       1-Butene          cis-2-Pentene
           Particulates (PM10)         cis-2-Butene      trans-2-Pentene
                                        Ethane            Propane
                                        Ethene            Propene
                                        Ethyl benzene     Toluene
                                        n-Heptane         m+p-Xylene
                                        n-Hexane          o-Xylene




Air Pollution Bandings and Health Issues

Banding     Index Health Descriptor
            1
                     Effects are unlikely to be noticed even by individuals who know they
Low         2
                     are sensitive to air pollutants
            3
            4
                     Mild effects, unlikely to require action, may be noticed amongst
Moderate 5
                     sensitive individuals.
            6
            7        Significant effects may be noticed by sensitive individuals and action
                     to avoid or reduce these effects may be needed (e.g. reducing
            8
High                 exposure by spending less time in polluted areas outdoors).
                     Asthmatics will find that their 'reliever' inhaler is likely to reverse the
            9
                     effects on the lung.
Very                 The effects on sensitive individuals described for 'High' levels of
            10
High                 pollution may worsen.



Boundaries Between Index Points for Each Pollutant
Band Index Ozone             Nitrogen      Sulphur       Carbon         PM10
                             Dioxide       Dioxide       Monoxide       Particles
             8       hourly
                                           15   minute 8        hour 24   hour
             running mean hourly    mean
                                           mean        running mean running
             or      hourly
                                                                     mean
             mean*
              µgm-           µgm-          µgm-          mgm-
                     ppb            ppb           ppb            ppm    µgm-3
             3               3             3             3
Low
                                                                 0.0-
       1     0-32    0-16    0-95   0-49   0-88   0-32   0-3.8          0-16
                                                                 3.2
                             96-    50-    89-    33-    3.9-    3.3-
       2     33-66 17-32                                                17-32
                             190    99     176    66     7.6     6.6
                             191-   100-   177-   67-    7.7-    6.7-
       3     67-99 33-49                                                33-49
                             286    149    265    99     11.5    9.9
Moderate
             100-            287-   150-   266-   100-   11.6-   10.0-
       4             50-62                                             50-57
             126             381    199    354    132    13.4    11.5
             127-            382-   200-   355-   133-   13.5-   11.6-
       5             63-76                                             58-66
             152             476    249    442    166    15.4    13.2
             153-            478-   250-   443-   167-   15.5-   13.3-
       6             77-89                                             67-74
             179             572    299    531    199    17.3    14.9
High
             180-    90-     573-   300-   532-   200-   17.4-   15.0-
       7                                                               75-82
             239     119     635    332    708    266    19.2    16.5
             240-    120-    363-   333-   709-   267-   19.3-   16.6-
       8                                                               83-91
             299     149     700    366    886    332    21.2    18.2
             300-    150-    701-   367-   887-   333-   21.3-   18.3-
       9                                                               92-99
             359     179     763    399    1063   399    23.1    19.9
Very High
             360     180     764    400    1064   400    23.2
                                                                 20 or 100      or
       10    or      or      or     or     or     or     or
                                                                 more more
             more    more    more   more   more   more   more
* For ozone, the maximum of the 8 hourly and hourly mean is used to calculate the
index value.




EC Threshold/Limit Values
                                                                        Value     µg/m3
Pollutant     Description            Criteria Based on
                                                                        (ppb)

              Vegetation Protection 1 hour mean                         200 (100)
Ozone
              Threshold             24 hour (daily) mean                65 (32)
Nitrogen
              Alert Threshold        3 hour mean                        400 (500)
Dioxide
              Alert Threshold        3 hour mean                        500 (188)
                                                                        80 (30) if smoke
                                     Median of daily       values   for concs    >    34
                                     pollution year (1)                 120(45) if smoke
                                                                        <=34

Sulphur                                                                 130 (49) if smoke
Dioxide                              Median of     daily   values   for concs     >    51
              Limit Value
                                     winter (2)                         180 (68) if smoke
                                                                        concs <=51
                                                                     250 (94) if smoke
                                     98th percentile of daily values concs    >     128
                                     for pollution year (3)          350 (131) if smoke
                                                                     concs <=128


Note:

   1. Sulphur dioxide measurements are reported over a pollution year (1 April - 31
      March) so that measurements include a continuous 6 month winter period. This is
      because these concentrations are generally higher during the winter months.
   2. Winter is defined as 1 Oct - 31 Mar

				
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