Editing Noise pollution (section)

===Instrumentation===
[[File:Sound level meter with sound waves.png|alt=|thumb|upright|A [[sound level meter]] is one of the main tools for measuring sounds in the environment and the workplace.]]

====Sound level meters====
Sound can be measured in the air using a [[sound level meter]], a device consisting of a microphone, an [[amplifier]], and a time meter.<ref>{{cite book |last1=Webster |first1=Roger C. |title=Plant Engineer's Handbook |year=2001 |isbn=978-0-7506-7328-0 |pages=707–719 |chapter=Noise and Vibration |doi=10.1016/b978-075067328-0/50044-6}}</ref> Sound level meters can measure noise at different frequencies (usually A- and C-weighted levels).<ref name=":02" /> There are two settings for response time constants, fast (time constant = 0.125 seconds, similar to human hearing) or slow (1 second, used for calculating averages over widely varying sound levels).<ref name=":02" /> Sound level meters meet the required standards set by the International Electrotechnical Commission (IEC)<ref>{{Cite web |title=IEC 61672-1:2013 {{!}} IEC Webstore |url=https://webstore.iec.ch/publication/5708 |url-status=live |archive-url=https://web.archive.org/web/20210126101227/https://webstore.iec.ch/publication/5708 |archive-date=2021-01-26 |access-date=2020-11-29 |website=webstore.iec.ch}}</ref> and in the United States, the American National Standards Institute as type 0, 1, or 2 instruments.<ref name=":13">{{Cite web |date=1983 |title=ANSI S1.4-1983, Specification for Sound Level Meters |url=https://law.resource.org/pub/us/cfr/ibr/002/ansi.s1.4.1983.pdf |url-status=live |archive-url=https://web.archive.org/web/20210211011219/https://law.resource.org/pub/us/cfr/ibr/002/ansi.s1.4.1983.pdf |archive-date=2021-02-11 |access-date=2020-11-28 |website=American National Standards Institute}}</ref>

Type 0 devices are not required to meet the same criteria expected of types 1 and 2 since scientists use these as laboratory reference standards.<ref name=":13" /> Type 1 (precision) instruments are to study the precision of capturing sound measurements, while type 2 instruments are for general field use.<ref name=":13" /> Type 1 devices acceptable by the standards have a margin of error of ±1.5&nbsp;dB, while type 2 instruments meet a margin of error of ±2.3&nbsp;dB.<ref name=":13" />

====Dosimeters====
Sound can also be measured using a [[noise dosimeter]], a device similar to a sound level meter. Individuals have used dosimeters to measure personal exposure levels in occupational settings given their smaller, more portable size. Unlike many sound level meters, a dosimeter microphone attaches to the worker and monitors levels throughout a work shift.<ref name=":14">{{cite report |url=https://www.cdc.gov/niosh/docs/98-126/pdfs/98-126.pdf?id=10.26616/NIOSHPUB98126 |title=Criteria for a recommended standard... occupational noise exposure, revised criteria 1998 |date=June 1998 |publisher=U.S. Department of Health and Human Services. National Institute for Occupational Safety and Health |doi=10.26616/NIOSHPUB98126 |id=DHHS (NIOSH) Publication No. 98–126 |access-date=2022-12-06}}</ref> Additionally, dosimeters can calculate the percent dose or time-weighted average (TWA).<ref name=":14" />

====Smartphone applications====
[[File:NoiseLevel LeafBlower.jpg|thumb|upright|alt=Noise level from a leaf blower using the NIOSH Sound Level Meter app showing 95.3 decibels.|Measuring the noise level from a leaf blower using the NIOSH Sound Level Meter app]]

In recent years, [[Scientist|scientists]] and [[Audio engineer|audio engineers]] have been developing smartphone apps to conduct sound measurements, similar to the standalone sound level meters and dosimeters. In 2014, the National Institute for Occupational Safety and Health (NIOSH) within the Centers for Disease Control and Prevention (CDC) published a study examining the efficacy of 192 sound measurement apps on Apple and Android smartphones.<ref name=":23">{{Cite web |date=2020-06-22 |title=NIOSH Sound Level Meter App {{!}} NIOSH {{!}} CDC |url=https://www.cdc.gov/niosh/topics/noise/app.html |url-status=live |archive-url=https://web.archive.org/web/20210901130051/https://www.cdc.gov/niosh/topics/noise/app.html |archive-date=2021-09-01 |access-date=2020-11-27 |website=www.cdc.gov |language=en-us}}</ref><ref name=":10">{{cite journal |vauthors=Kardous CA, Shaw PB |date=April 2014 |title=Evaluation of smartphone sound measurement applications |journal=The Journal of the Acoustical Society of America |volume=135 |issue=4 |pages=EL186–EL192 |bibcode=2014ASAJ..135L.186K |doi=10.1121/1.4865269 |pmc=4659422 |pmid=25236152}}</ref>

The authors found that only 10 apps, all of which were on the [[App Store (iOS/iPadOS)|App Store]], met all acceptability criteria. Of these 10 apps, only 4 apps met accuracy criteria within 2&nbsp;dB(A) from the reference standard.<ref name=":23" /><ref name=":10" /> As a result of this study, they created the NIOSH Sound Level Meter App to increase accessibility and decrease costs of monitoring noise using crowdsourcing data with a tested and highly accurate application.<ref name=":23" /><ref name=":10" /> The app is compliant with ANSI S1.4 and IEC 61672 requirements.<ref>{{Cite journal |vauthors=Celestina M, Hrovat J, Kardous CA |date=2018-10-01 |title=Smartphone-based sound level measurement apps: Evaluation of compliance with international sound level meter standards |journal=Applied Acoustics |language=en |volume=139 |pages=119–128 |doi=10.1016/j.apacoust.2018.04.011 |s2cid=116822722}}</ref>

The app calculates the following measures: total run time, instantaneous sound level, A-weighted equivalent sound level (LAeq), maximum level (LAmax), C-weighted peak sound level, time-weighted average (TWA), dose, and projected dose.<ref name=":23" /> Dose and projected dose are based on sound level and duration of noise exposure in relation to the NIOSH recommended exposure limit of 85&nbsp;dB(A) for an eight-hour work shift.

Using the phone's internal microphone (or an attached external microphone), the NIOSH Sound Level Meter measures instantaneous sound levels in real time and converts sound into electrical energy to calculate measurements in A-, C-, or Z-weighted decibels. App users are able to generate, save, and e-mail measurement reports. The NIOSH Sound Level Meter is currently only available on Apple iOS devices.