Comparing Indoor Air Quality Targets: What "Clean" Means Around the World - PM2.5 and PM10

Across the world, buildings that all claim to have "good" indoor air can have very different air. A building that passes one national standard can have ten times more fine particles than one certified under a health-focused framework, and both are considered compliant.

This comparison looks at 17 government standards and building certifications from North America, Europe, and Asia-Pacific to show where they agree, and where they diverge.

About This Series

This article is Part 1 of 4 in the IAQ Target Comparison Series. We are splitting the full master comparison into four focused articles for readability:

• Part 1 — Particulate Matter: PM2.5 & PM10

• Part 2 — Carbon Gases: CO2 + CO

• Part 3 — Organic Chemicals: TVOC + Formaldehyde

• Part 4 — Inorganic Gases & Radon: Ozone, Nitrogen Dioxide, Sulfur Dioxide, and Radon

Standards referenced in this article (17 total): WHO 2021, EPA NAAQS, EU Directive 2024/2881, Singapore SS 554 (2021), China GB/T 18883, RESET Air v2.0, LEED v5 O+M, WELL v2, BREEAM, Fitwel, Living Building Challenge (LBC), ASHRAE 62.1 (2022), DGNB, BOMA BEST, Singapore Green Mark, HKGBC BEAM Plus, and China Green Building Standard.

How to read this comparison

Averaging periods matter. Different standards use different averaging periods, and concentration limits should therefore be interpreted together with their corresponding exposure durations. In this report, Annual limits are presented separately, while Daily and Unspecified limits are grouped together to reduce the number of charts and improve readability. It is important to note that Unspecified does not mean equivalent to Daily; it only indicates that the standard does not explicitly define an averaging period.

• Daily: Workday or daily exposure

• Annual: Long-term chronic exposure

• Unspecified: Standard does not state an averaging period

Type: Each standard is marked as Government (national codes, regulations, guidelines) or Certification (voluntary building certification or private framework).

Particulate Matter: PM2.5 and PM10

PM2.5 (Daily & Unspecified)

Summary

• Range: 10 to 75 µg/m³, a 7.5-fold gap, across 20 limits. This is the densest comparison in the dataset.

• Strictest: WELL Enhanced (2 pts) at 10 µg/m³, but it does not specify it's averaging time (UNS). The strictest with a specified averaging time is RESET (High Performance), LEED v5 O+M (4 pts), Fitwel, and LBC at 12 µg/m³.

• Most common value: 12 µg/m³, where five certifications converge: LEED v5 O+M (4 pts, 24H), WELL Enhanced 1 pt (UNS), Fitwel (24H), LBC (UNS), and RESET High Performance (24H).

• WHO alignment point: WHO AQG at 15 µg/m³ (24H, Government) aligns with LEED v5 O+M (3 pts) and WELL Acceptable, showing where certifications meet the WHO guideline.

• Mid-range progression: Steps through WHO Interim 4 and WELL Modified at 25 µg/m³, EU Directive 2024/2881 (By 2030) at 25 µg/m³ (UNS), RESET Acceptable and EPA NAAQS at 35 µg/m³ (24H), and WHO Interim 3 SS 554 SG Green Mark at 37.5 µg/m³ (24H).

• Upper end: WHO Interim 2 and China GB/T 18883-2022 at 50 µg/m³ (24H) and WHO Interim 1 at 75 µg/m³ (24H).

• Type split: Certifications dominate the low end (10-15 µg/m³), Government standards define the full progression from 15 to 75 µg/m³.

PM2.5 (Annual)

Summary

• Range: 5 to 35 µg/m³, a 7-fold gap, across 13 limits.

• Strictest: WHO AQG at 5 µg/m³ (Annual, Government).

• Most common value: 10 µg/m³ and 25 µg/m³, each with three standards. At 10 µg/m³: WHO Interim 4 (Government), Directive (EU) 2024/2881 By 2030 (Government), and DGNB Low Danger (Certification). At 25 µg/m³: WHO Interim 2 (Government), Directive By 2026 (Government), DGNB High Danger (Certification), and China Green Building Std (Certification) — four at 25.

• Mid-range progression: Steps through EPA NAAQS Primary and ASHRAE 62.1 at 9 µg/m³ (Annual), 10 µg/m³ cluster, then WHO Interim 3 and EPA NAAQS Secondary at 15 µg/m³ (Annual).

• Upper end: WHO Interim 1 at 35 µg/m³ (Annual, Government).

• Type split: Government defines the WHO ladder (5 to 35 µg/m³) and EU 2030/2026 targets (10 and 25 µg/m³) and both EPA NAAQS levels. Certifications mark low/high danger at 10 and 25 µg/m³ (DGNB), 9 µg/m³ (ASHRAE 62.1), and 25 µg/m³ (China Green Building Std).

PM10 (Daily & Unspecified)

Summary

• Range: 20 to 150 µg/m³, a 7.5-fold gap, across 16 limits.

• Strictest: WELL Enhanced (2 pts) at 20 µg/m³, but it does not specify it's averaging time (UNS). The strictest with a specified averaging time is WHO (AQG) at 45 µg/m³.

• Most common value: 50 µg/m³, where five standards converge: WHO Interim 4 (24H), Directive (EU) 2024/2881 By 2026 (24H), LEED v5 O+M (24H), and WELL v2 Acceptable & Modified (UNS).

• WHO alignment point: WHO AQG at 45 µg/m³ (24H, Government) aligns with Directive (EU) 2024/2881 By 2030, showing EU alignment with WHO.

• Mid-range progression: Steps through 45 µg/m³ (WHO AQG / EU 2030), 50 µg/m³ cluster, then WHO Interim 3 at 75 µg/m³ (24H).

• Upper end: WHO Interim 2 and China GB/T 18883-2022 at 100 µg/m³ (24H), WHO Interim 1 and EPA NAAQS at 150 µg/m³ (24H), and BOMA BEST at 150 µg/m³ (UNS).

• Type split: Certifications dominate the low end (20-30 µg/m³), Government standards define the progression from 45 to 150 µg/m³, with LEED v5 O+M included at 50 µg/m³ (24H).

PM10 (Annual)

Summary

• Range: 15 to 70 µg/m³, a 4.7-fold gap, across 10 limits.

• Strictest: WHO AQG at 15 µg/m³ (Annual, Government).

• Most common value: 20 µg/m³, where three standards converge: WHO Interim 4 (Annual, Government), Directive (EU) 2024/2881 By 2030 (Annual, Government), and DGNB Low Danger (Annual, Certification).

• Mid-range progression: Steps through WHO Interim 3 at 30 µg/m³ (Annual), then Directive (EU) 2024/2881 By 2026 and DGNB High Danger at 40 µg/m³ (Annual), and WHO Interim 2 / China Green Building Std at 50 µg/m³ (Annual).

• Upper end: WHO Interim 1 at 70 µg/m³ (Annual, Government).

• Type split: Government standards define the full WHO interim ladder (15 to 70 µg/m³) and EU targets, Certifications mark low-danger and high-danger thresholds at 20 and 40 µg/m³ (DGNB) and 50 µg/m³ (China Green Building Std).

Conclusion: What PM Targets Tell Us

PM2.5 and PM10 reveal a clear split between aspirational and regulatory air quality:

• Certifications drive stringency: The lowest limits typically come from building certifications instead of governments.

• Averaging matters: There are differences between Daily (daily operation) and Annual (chronic exposure) numbers, which makes assigning averaging times really important. Targets should always have an averaging time and not remain unspecified (UNS).

• Unified Targets: Based on the targets, an optimal design is for a PM2.5 Target of 12 µg/m³ (Daily) and 9-10 µg/m³ (Annual). For PM10 targets, 45 µg/m³ (Daily) and 20 µg/m³ (Annual). With these targets, a project can satisfy 5+ certifications and sit within striking distance of WHO AQG.

In Part 2, we apply this same lens to CO2 + CO.

Appendix: Standards List and resources for Particulate Matter

Government standards, codes, and guidelines (5 total):

• World Health Organization (WHO). WHO Global Air Quality Guidelines: Executive Summary. p. 4.

• US EPA NAAQS — National Ambient Air Quality Standards: NAAQS Table

• EU Directive 2024/2881: EU Directive 2024/2881, Annex I

• Singapore SS 554 (2021) : SS 554:2016+A1:2021 Code of Practice for Indoor Air Quality for Air-Conditioned Buildings. p. 20.

• China GB/T 18883-2022: GB/T 18883-2022 室内空气质量标准. p. 3.

Building certifications and private frameworks (10 total):

• RESET Air v2.0: RESET Air Standard.

• LEED v5 O+M: LEED v5 Reference Guide for Building Operations and Maintenance. November 2025 Edition, pp. 67–68.

• WELL v2: The WELL Building Standard v2.

• Fitwel: Fitwel v3 Indoor Air Quality Assessment Protocol. p. 13.

• Living Building Challenge (LBC): Living Building Challenge 4.1 Program Manual. January

• ASHRAE 62.1 (2022): ANSI/ASHRAE Standard 62.1-2022: Ventilation for Acceptable Indoor Air Quality. 2022, p. 1.

• DGNB: DGNB System – Buildings In Use, Criteria Set Version 2026. 2026, pp. 98–99.

• BOMA BEST: BOMA BEST Field Guide.

• Singapore Green Mark: SS 554:2016+A1:2021 Code of Practice for Indoor Air Quality for Air-Conditioned Buildings. p. 20.

• China Green Building Standard: 《绿色建筑评价标准》. 2024, p. 6.