Fine dust alarm

Fine particulate matter (PM10) consists of tiny particles less than one-tenth the diameter of a hair. PM stands for Particulate Matter and 10 for the largest dust particle diameter in micrometers - that is, one hundred thousandth of a meter - found in particulate matter. Particulate matter is primarily generated by human activity: it is created by emissions from motor vehicles, electricity and thermal energy generation, and residential furnaces and heaters, among other sources. However, there are also natural sources such as dust stirring up from soils or pollen drift.

In large cities, road traffic is a major source of particulate matter. The particulate matter from traffic is mainly generated by brake and tire abrasion as well as by dust being stirred up from the road surface, and secondarily by exhaust gases from conventionally operated internal combustion engines.

The effect of these microscopically fine particles is great: they enter the human organism via the lungs and can cause respiratory problems as well as diseases of the cardiovascular system. Scientists have proven that the very finest dust particles are even transported into the blood circulation, the heart, the liver and other organs and can even penetrate into the brain. Particularly for children, fine dust can have serious consequences.

In 2018 and 2019, the legal particulate matter limits were complied with at all air measuring stations in the city area - i.e. also at Neckartor. In 2018, the Landesanstalt für Umwelt Baden-Württemberg (LUBW) recorded 20 days of exceedance gravimetrically at the measuring station "Am Neckartor", in 2019 there were 27 days of exceedance. Legally permissible are 35 exceedance days above 50 micrograms per cubic meter of air per year. In 2017 there were 41 exceedance days, in 2016 there were 58 exceedance days (road salt and natural sources already deducted in each case). The permissible annual average limit of 40 micrograms per cubic meter of air has been reached at all stations since 2011.

A significant proportion of the particulate matter emissions measured in Stuttgart originate from wood combustion. The wood-burning fireplaces and stoves in private households in Stuttgart make a relevant contribution to particulate matter pollution as the second largest polluter after road traffic.

The state of Baden-Württemberg therefore passed an ordinance on operating restrictions for small combustion plants (Air Quality Ordinance-Small Combustion Plants) in January 2017. The operating ban came into force on February 24, 2017.

Accordingly, comfort fireplaces may not be operated in accordance with Section 2 (1) of the Ordinance of the State Government on Operating Restrictions for Small Combustion Plants (Air Quality Ordinance-Small Combustion Plants) of January 31, 2017, if there is a risk that the immission limit value for particulate matter (PM 10) averaged over the day for the Stuttgart municipal area will be exceeded. The ban on operation applies in the winter half-year from October 15 to April 15 on days when there is a risk of the limit being exceeded, as soon as the general ruling is in force.

The ban relates to single-room furnaces for solid fuels (for example, wood) that are operated in addition to another heating system, such as a central heating system, and thus serve only as an additional source of heat. The basic supply is not affected.

Exemptions for comfort fireplaces that have been retrofitted with a downstream dust reduction device (particle separator) may be granted upon application.

Further information:

The fine dust alarm was a unique instrument used by the state capital Stuttgart throughout Germany to provide information about the air situation in Stuttgart and to call on citizens to switch to sustainable means of transport.

The fine dust alarm was triggered as soon as the German Meteorological Service (DWD) forecast a severely restricted exchange capacity of the atmosphere for at least two consecutive days.

Meteorologists refer to this as a so-called low-exchange weather situation: warm air in the higher air layers prevents air from rising from the ground and thus vertical exchange. At the same time, there is little or no wind, so that exchange in the horizontal direction is also strongly suppressed. In the urban basin and valleys, this makes it difficult or impossible for polluted air to dilute. As a result, air pollutants near the ground can no longer be removed. On these days, the concentration of particulate matter rises sharply. There is a risk that the limit values will be exceeded.

The state of Baden-Württemberg, the regional council and the city of Stuttgart have therefore appealed to the population in Stuttgart and the metropolitan region during fine dust alerts not to use their cars in the Stuttgart urban area if possible and to refrain from operating comfort fireplaces. Drivers were advised to switch to public transport or the bicycle, to walk or to carpool.

Likewise, those who had the opportunity should work from home or take advantage of flexible work schedules in arrangements with their employers. Commuters were advised to switch from their cars to the rail network and to take advantage of the park-and-ride facilities in the VVS area.

In addition, there were a variety of offers from different players that facilitated a switch to sustainable means of transport, including discounts. The state capital Stuttgart also enabled its employees to work more flexibly during the fine dust alert.

The fine dust alarm could last for several days, but at least for two consecutive days. To lift the fine dust alert, the German Meteorological Service (DWD) had to predict a sustained and significant improvement in the exchange capacity; a one-day interruption of the severe restriction of the exchange capacity was not sufficient in this respect.

Low-exchange weather conditions are a particular problem in winter, as these weather conditions occur more frequently during this time of year and favor the accumulation of pollutants near the ground. The German Meteorological Service (DWD) defined the exchange capacity for declaring a fine dust alarm based on the following criteria:

1. particulate matter concentration more than 30 micrograms per cubic meter at Neckartor and lack of rain.
2. absence of rain
3. absence of effective wind from a favorable direction
4. nocturnal soil inversion
5. shallow mixing layer during the day
6. low wind speed

Basically, the exchange capacity depended on the number and combination of fulfilled criteria. However, criterion 1 (particulate matter concentration > 30 µg/m³ and lack of rainfall) was a priority fulfillment criterion. That is, meeting this criterion was sufficient to trigger the particulate matter alarm.

If criterion 1 had not been met, at least four of the other criteria had to be present for the exchange capacity to be classified by DWD as severely limited. Criteria 2 (lack of rain) and 3 (lack of effective wind from a favorable direction) and at least one of criteria 4 (nighttime soil inversion) or 5 (shallow mixed layer) had to be mandatory. Criterion 6 (low wind speed) had to be met if only one of criteria 4 or 5 was present.

Yes, that was quite possible. Weather conditions are only one controlling factor when it comes to the level of particulate matter pollution. In addition to meteorological influences, increased traffic volume or heavy emissions from heating systems also contribute to limit value exceedances. The city triggered the fine dust alarm on the basis of a weather forecast or the pre-pollution at the measuring point "Am Neckartor": Based on six criteria developed together with the German Weather Service (DWD), the exchange capacity of the atmosphere was evaluated (see above). This procedure did not provide absolute prediction certainty, since the fine dust load could not be predicted. Nevertheless, it was possible to predict with a very high probability whether the weather situation contributed to increased particulate matter levels or not.

In order to reduce pollution in Stuttgart and continue to keep it low, every single citizen can do their part. This includes, for example, the following possibilities:

• Using public transportation: The city of Stuttgart has a dense and well-functioning network of bus, light rail and S-Bahn lines. Over 900,000 people use public transportation in Stuttgart every day - and the numbers are rising. The service is therefore being continuously expanded.
• P+R parking: Practical for commuters who want to switch from the car to the rail network: In the VVS area, more than 17,000 parking spaces are available at 217 park-and-ride (P+R) facilities. an overview of P+R facilities in and outside the city area can be found here.
• Carpool: On average, a car in Stuttgart is occupied by only 1.23 people. Car pooling is therefore a sensible way to reduce motorized traffic in Stuttgart and the metropolitan region and to use the car more efficiently. Mediation exchanges on the Internet help to find the right carpool member.
• Riding a bicycle or pedelec: The cycling network is continuously being expanded and improved in Stuttgart. If you don't have your own bike, you can use the RegioRadStuttgart, for example.
• Riding an (electric) car, e-scooter or e-scooter: Various providers allow the rental of electric vehicles in Stuttgart - whether car, scooter or scooter.
• Simply walking: More than 30 percent of all daily trips in Stuttgart are made on foot. Walking is healthy, environmentally friendly and it costs nothing. An overview of which destinations in the city center can be reached quickly on foot is available here.
• Make work flexible: Why not leave for work earlier or later? Many companies offer flextime, helping to ease the burden on public transportation during rush hours.
• Reduce leisure travel: You can also actively contribute to better air in Stuttgart during your free time. Your own district often offers many opportunities for sports, recreation and relaxation. If you take advantage of the local offers, you not only strengthen the district, but also avoid longer journeys and thus traffic.
• Skip the comfort fireplace: In January 2017, the state of Baden-Württemberg passed an ordinance on operating restrictions for small combustion plants (Air Quality Ordinance-Small Combustion Plants). This prohibits the operation of so-called comfort fireplaces on days when there is a risk of the limit value being exceeded in the Stuttgart urban area.

Nitrogen dioxide (NO2), like particulate matter, is formed during combustion processes, but only at high combustion temperatures, by oxidation of atmospheric nitrogen. The main sources are conventionally operated combustion engines, especially diesel engines without effective denitrification techniques. Combustion plants for coal, oil, gas, wood and waste also emit nitrogen dioxide. But in urban areas such as Stuttgart, road traffic is a significant NO2 polluter.

Nitrogen dioxide can cause inflammatory reactions in the respiratory tract and increase the irritant effects of other air pollutants. With prolonged exposure, higher concentrations can lead to chronic bronchitis or even an increase in susceptibility to respiratory infections. High NO2 concentration is especially a problem for asthmatics, as it can lead to bronchoconstriction. All nitrogen oxides also have a toxic effect on plants, as they damage the upper layer of leaves and needles in trees, for example. They also play a decisive role in the formation of so-called summer smog. When exposed to heat and solar radiation, they react to form ozone, an irritant gas like NO2 itself.

Europe-wide limits have also been set for nitrogen dioxide. Allowed are 18 hours of exceedance at a limit of 200 micrograms per cubic meter of air. The limit was exceeded on two hours in 2019, according to official measurements by LUBW. In 2018, there were eleven hours of exceedance, in 2017 there were three and in 2016 there were 35. At all other measuring points, this limit value is now complied with.

In contrast to particulate matter, however, the annual mean value is problematic for nitrogen dioxide, which still exceeds the legal limit despite improvements. The annual mean limit is 40 micrograms per cubic meter of air. At the "Am Neckartor" measuring point, the Baden-Württemberg State Institute for the Environment recorded an annual mean value of 53 micrograms per cubic meter of air for 2019. In 2018, the value was still 71 micrograms, in 2017 73 and in 2016 82. The permissible NO2 annual mean value is also exceeded at the measuring points "Hohenheimer Straße" (50 micrograms per cubic meter of air in 2019) and "Arnulf-Klett-Platz" (40 micrograms per cubic meter of air in 2019). Due to the high values, the state of Baden-Württemberg has issued various traffic bans for diesel vehicles in its updates of the clean air plan for the state capital Stuttgart. Detailed information is available at  www.stuttgart.de/diesel-verkehrsverbot.

Further information:

Stuttgart has been an environmental zone since March 1, 2008. This means that only vehicles with emission class 4 are now allowed to enter the Stuttgart city area. These vehicles have a green environmental sticker. With this sticker, all environmental zones may be entered without restriction. Vehicles belonging to pollutant groups 1, 2 and 3 (vehicles with a red or yellow sticker) are prohibited from driving in Stuttgart.

Air pollution in Stuttgart varies greatly depending on the pollutant. For example, the limit values for sulfur dioxide and carbon monoxide are significantly undercut. The levels of these air pollutants are not critical. The problem is particularly the more traffic-related pollutants particulate matter (PM10) and nitrogen dioxide (NO2).

The "thick air" is mainly due to two reasons:

• Due to the city's topographical location, there is relatively little air movement in the downtown area. In any case, the entire region is considered to have little wind. Particularly in the colder months of the year, the problem of so-called low-exchange weather conditions therefore occurs frequently: The air can no longer circulate and air pollutants are not removed.
• Added to this is the high volume of traffic in the city. Especially the streets with heavy traffic are polluted by air pollutants.
  

The Stuttgart municipal boundary is crossed around 912,000 times within 24 hours by vehicles entering or leaving the city (last count 2018). Under the simplified assumption that each vehicle travels only once in each direction, that is around 455,000 vehicles.

Every two years, the city also conducts what is known as a kettle edge count. In this survey, traffic is counted at 21 prominent locations on the edge of the city center, including the B14 Cannstatter Straße and the B27 Neue Weinsteige. In the current count in 2019, 418,000 motor vehicles entering and leaving Stuttgart were counted at the "Kesselrand". The number has been declining slightly for years, although the number of inhabitants in Stuttgart and the region is continuously increasing.

Currently, 301,373 passenger cars are registered in Stuttgart (as of June 30, 2020).

More than 58% of the particulate matter concentration at Neckartor is caused by road traffic. This value is made up of the exhaust gas immission share (7%) and the immission shares due to swirling and tire, brake and road abrasion (45%) or secondary immission (6.2%). Small and medium-sized combustion plants (e.g. comfort fireplaces) have a share of just under 8%, while industry, off-road traffic and other technical facilities contribute 7% to the load.

At Neckartor, 78% of the nitrogen dioxide (NO2) pollution is caused by road traffic. Small and medium combustion plants have a total share of 12%. The source groups industry, off-road traffic and other technical facilities contribute with 3% to the pollution.