Editing Rolling mean in ozone exceedance days

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|+ SIGNAL Earth Structured Data
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! Object type
| Damage Signal
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! SIGNAL Earth ID
| DS-00559
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! Observable type
| Ground-level ozone concentration (ambient)
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! Unit
| µg/m³ (or ppb) (ambient ozone concentration)
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! Temporal structure
| Hourly/Daily
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! Monitoring backbone
| Air quality monitoring networks + reanalysis
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The {{SignalTerm|type=DS|id=DS-00559|label=Rolling mean in ozone exceedance days}} is an environmental indicator derived from measurements of ground-level ozone concentration. It quantifies the average number of days within a specified rolling period during which ozone levels surpass established health or ecological thresholds. This metric provides insight into the temporal patterns and persistence of elevated ozone conditions, which are relevant for assessing air quality impacts on human health, vegetation, and ecosystems.

Ground-level ozone is a reactive chemical species formed through photochemical reactions involving precursor pollutants such as nitrogen oxides and volatile organic compounds. Elevated ozone concentrations near the Earth's surface can contribute to respiratory problems in humans and damage to crops and natural vegetation. Monitoring exceedance days helps to characterize the frequency and duration of potentially harmful ozone exposure events.

This signal is part of a broader global effort to understand and manage air pollution, supported by extensive air quality monitoring networks and atmospheric reanalysis datasets. It provides a standardized approach to tracking changes in surface ozone exposure over time and across different regions worldwide.

== Geographic / System Context ==
Ground-level ozone concentrations and their exceedance patterns vary geographically due to differences in emission sources, meteorological conditions, and topography. This signal encompasses a global scope, capturing data from urban, rural, and remote locations across continents and oceanic regions. Regions with high industrial activity, dense transportation networks, and specific climatic conditions often exhibit more frequent exceedance days. Conversely, areas with low precursor emissions or favorable atmospheric dispersion conditions typically experience fewer exceedances. The global perspective allows for comparative assessments of ozone pollution and its environmental implications across diverse geographic systems.

== Monitoring and Measurement ==
Monitoring of ground-level ozone concentration is conducted through a combination of in situ air quality monitoring stations and atmospheric reanalysis products. Established air quality networks operated by governmental and research institutions provide high temporal resolution measurements, often hourly, using standardized methods such as ultraviolet photometry. Reanalysis datasets integrate observational data with atmospheric models to generate spatially continuous ozone concentration fields. Thresholds for exceedance days are defined based on health guidelines or ecological criteria established by organizations such as the World Health Organization ([https://en.wikipedia.org/wiki/World_Health_Organization WHO]). The rolling mean is calculated by averaging the count of exceedance days over a moving window, typically spanning several days to weeks, to smooth short-term variability and highlight trends.

Within the SIGNAL system, this phenomenon is treated as a defined environmental signal whose boundaries and measurement conventions are described below.

== Signal Definition ==
The rolling mean in ozone exceedance days measures the average number of days within a specified rolling period during which the ambient ground-level ozone concentration exceeds a predefined threshold. The observable quantity is the ground-level ozone concentration, expressed in micrograms per cubic meter (µg/m³) or parts per billion (ppb). The temporal resolution of the underlying data is hourly or daily, enabling identification of exceedance events on a daily basis. The rolling mean aggregates these daily exceedance counts over a moving time window to characterize the persistence and frequency of elevated ozone conditions.

== Boundary Conditions ==
Boundary inclusions encompass all days within the rolling period where measured or modeled ground-level ozone concentrations surpass the threshold established for health or ecological concern. This includes exceedances detected at any monitoring location within the geographic scope. Boundary exclusions comprise days where ozone concentrations remain below the threshold, as well as data points lacking sufficient measurement quality or temporal coverage. The signal excludes ozone levels measured above the surface layer, focusing solely on ambient ground-level concentrations relevant to human and ecosystem exposure. Temporal boundaries are defined by the length of the rolling window, which may vary depending on application but typically ranges from one week to one month.

== Aggregation Semantics ==
Geographic aggregation involves compiling exceedance day counts from multiple monitoring sites within defined spatial units, such as cities, regions, or countries, to produce area-representative rolling mean values. Temporal aggregation uses a moving average approach over a specified window (e.g., 7 or 30 days) to smooth daily exceedance variability and reveal trends. Cross-signal aggregation may incorporate this signal alongside related air quality indicators, such as nitrogen dioxide or particulate matter exceedances, to assess combined pollutant impacts. Aggregation notes emphasize the importance of consistent threshold definitions and data completeness to ensure comparability across space and time.

== Observational Status ==
The rolling mean in ozone exceedance days is actively monitored through extensive air quality networks and supported by global reanalysis products. Data availability varies regionally, with higher density in developed areas and sparser coverage in remote regions. Current SIGNAL releases incorporate standardized exceedance calculations based on established thresholds, facilitating global assessments of ozone pollution episodes. Future updates may expand temporal coverage, refine threshold criteria, and integrate additional observational platforms to enhance spatial resolution and data robustness.

== Related Signals ==
* None specified

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== Key Associated People ==
* '''David Parrish''' — Contributor (NOAA (emeritus)) [Domain expert]
* '''Owen Cooper''' — Contributor (NOAA Chemical Sciences Laboratory) [Domain expert]
* '''Pasquale Borrelli''' — Contributor (University of Basel) [Domain expert]
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== Sources ==
* [https://www.who.int/publications WHO / UNEP cyanobacteria & eutrophication guidance (context)]
* [https://toar-data.org/ TOAR global ozone database]
* [https://doi.org/10.1002/2013RG000431 Cooper et al. tropospheric ozone assessment]
* [https://igacproject.org/ IGAC tropospheric ozone assessment resources]
* [https://doi.org/10.1038/s41586-017-0529-7 Global Soil Erosion Assessment]
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