13.58 parts per billion is the average for Nitrogen Dioxide (NO2) in Sheffield air (all readings, all times of day/night , When monitor is working) This quiz tests your understanding of how the ppb figure varies over time

Shows average NO2 by hour of day/night. What do you notice? What might cause this?

Previous question suggested that human behaviour (driving?) can effect NO2 levels. One of the lines above is average NO2 for weekends, The other line is average NO2 for work days (Mon-Fri) Which is which?

The BLUE line is weekends The RED line is Monday-Friday. There is lower NO2 pollution levels at weekends.

Here are the average NO2 levels per hour, for each of the seven days From what you know about week-day and weekends, suggest which days the ORANGE and the LIGHT BLUE lines represent.

Notice the clean(er) air effect of a lack of “rush hour” traffic on Sundays Saturdays and Sundays do have afternoon peaks, but later in the afternoon than weekdays. What might be causing this?

It isn’t just human activity that affects NO2 levels. Weather plays a big part too. This graph shows the average NO2 level for different sets of air temperature. What does the graph tell you about how NO2 levels vary with temperature?

From the previous graph you should expect that WARMER DAYS have LOWER LEVELS of NO2 pollution. Here (again) is the graph showing average levels of pollution. This graph is for all days that the monitor was working. Sketch on the screen what line you would expect for a typical summer day

Is this what you sketched. The blue line is the average for all days in the year The green line is the average for JUNE (summer) days only. How much lower are the green readings?

The opposite is also true COLDER DAYS typically have HIGHER LEVELS of NO2 pollution. Again sketch on the screen, this time for what line you would expect for a typical winter day

This is what the monitor found The blue line is the average for all days in the year The red line is the average for JANUARY (winter) days only. The early morning values are the same. But from breakfast onwards, the values are 5 ppb higher most of the day.

Temperature is not the only thing that affects NO2 levels. Dampness in the air retains NO2 longer. Which of these three graphs is the correct one for showing that HIGH HUMIDITY typically relates to HIGHER NO2?

The correct graph for HIGH HUMIDITY  HIGHER NO2 is shown above (But.... On very dry sunny days the NO2 breaks down into Ozone, which is a pollutant with different nasty effects. So extremely low humidity isn’t good for clean air either)

Air Pressure has complicated link to NO2 levels. We won’t go into the detailed explanation. But what is the main observation from this graph.

Wind Speed also has an affect on pollution levels. For our monitor, it recorded worse NO2 levels on windless days. On windy days the pollution blows somewhere else But then some area would get higher pollution on higher wind days! So the effect of wind and pollution is different for each local situation.

From the previous slides, which of the following are (for our monitor) associated with HIGH NO2? Warm or Cold days? Dry or Humid air? Windy or Still days? High Pressure or Low Pressure? See what you can remember from the slides so far

In Sheffield there were 11 days during when whether was particularly COLD DAMP (humid) STILL HIGH PRESSURE Look at the dates. What time of year were these? Are the NO2 levels more than the average of ppb?

Now look at the hour-by-hour readings for these 11 days of cold/damp/still/pressured air. How many of the individual readings are above average of ? What is the longest sequence of hours where air quality was poor?

The answers are: EVERY reading within those conditions are high. The longest sequence was 3pm 13 th Jan 2010, to 4am the following day hours. What is the effect on human health of 13 hours of bad air?

EU Directive on NO2 levels

Sheffield : 10 days in where the whole-day average exceeded 40 ppb The worst full-day average was ppb.

Sheffield : But there were 37 days when just between 6pm – 7pm (evening rush hour) the levels were “unsafe” What was the worst reading in this time?

Overall there were 78 days with at least one hour of ‘unsafe’ levels out of the 1313 days when the monitor reported data What percentage is 78 out of 1313 (a) 1% (b) 6% (c) 13% (d) 20%

Answer 78 days with at least one hour of ‘unsafe’ levels out of the 1313 days when the monitor reported data is 6% What do YOU think? Are you happy that 6% of days in Sheffield have ‘unsafe’ levels of NO2 for at least part of the day?