Airwatch – Measuring visual air quality

1. Aim

The VAQ study described involves two parts

1. a photographic record over a number of days/weeks of the visual clarity of prominent target sites taken from a set location
   
2. a record of related weather observations for the target sites.
   

Observations are entered in a daily field recording sheet. Questions asked on the sheet are

• How would you rate the overall VAQ (360) at this time?
• How clearly can the observer see the objects in the distance?
• Is there something unusual which is affecting visual air quality today?
• What is the cloud cover in the present view path?
• What is the weather at your site ( weather station information )?
• What do you think the visibility range is at this time?

2. Choosing a set location

The location from which all the target sites are to be viewed must be elevated above the surrounding area so a clear unobstructed view can be obtained. Suitable locations include: a roof balcony with 360° views, a lookout on top of a hill, a window which overlooks lower land and for considerable distances. Unsuitable locations would be flat or low lying land where the view is obstructed by buildings.

3. Selecting the target sites to study

The key criteria in selecting a target site is that its view must be unobstructed. The target site should be a prominent feature such as a mountain/hill, buildings, a bridge, or an architectural feature such as a monument.

Select a number of target sites to give a range of distances from the location, eg., 5 km, 10 km, 15 km, 20 km, 25 km. Calculate the distances to the target sites by using map information available from Automobile Clubs in your area.

4. Method

• At the set location photograph the chosen target sites each day or chosen days. Make sure that you frame the site the same each time.

  (A SLR CAMERA is recommended; 200 ASA film)

• Complete a daily field recording sheet (Figure 3.).
  It is important that your assessment of the visual range of each target site should not be influenced by the meteorological conditions at the time. For example a mountain range or city building may not be visible due to intense cloud cover, fog or mist, rather than the levels of pollution in the air.
  Estimate the visual range by assessing which target sites are more visible than others. For example, a target building at 20 km from the set location may be difficult to see. A tower 10 km from the set location may be quite clear. The visibility or visual range is between 10 and 15 km.
• Gather weather station information for each day.
• If possible obtain nephelometer data from your local EPA and correlate what you have observed about visual air quality on any one day with their information.
• At the conclusion of the study period (for example, 10 days) display the photographs from the study (see Figure 1). Select days which show the greatest visual contrast. Attach a map to show the target site locations in relation to the set location and to each other.

Figure 1. An example of a display of results from a visual air quality study.

5. Field record sheet

An example field record sheet is given in Figure 3. Rows 2 to 6 ask you to rate the VAQ of each target site in different ways. The key to site rating is shown in Figure 2:

Figure 2. Key to ratings for field record sheet.

	Date and time Location	SITE 1 Name -	SITE 2 Name -	SITE 3 Name -	SITE 4 Name -	SITE 5 Name -
1	Distance from your location (km)	__	__	__	__	__
2	Rate your impression of the overall visual air quality at the present time (Rate 1-9)	__	__	__	__	__
3	How clearly can you see each site. (Is it sharply defined and details easy to see?) (Rate 1-4)	__	__	__	__	__
4	What is the cloud cover at present? (Rate 1-5)	__	__	__	__	__
5	What is the weather at the site? (Rate 1-5)	__	__	__	__	__
6	How windy is it today? (Rate 1-4) Record the wind speed (m s-1) and wind direction	__	__	__	__	__
7	Is the something unusual affecting visual air quality today? If YES, give details about the source. Is it close or distant?	__	__	__	__	__
8	Photograph (Yes/No) (photo number)	__	__	__	__	__

Figure 3. Field Record Sheet

Contact: peter.manins@csiro.au

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Modified: 16 May 2002