# What Is AUS 40? The Complete Guide to Marine Urea Solution

**AUS 40 (Aqueous Urea Solution 40%)** is a clear, colourless solution of 40% high-purity urea by mass in demineralised water. It is the reductant consumed by Selective Catalytic Reduction (SCR) systems on marine diesel engines, converting NOx into harmless nitrogen and water. Also called: marine urea, marine urea solution, marine DEF, SCR reagent, marine NOx reduction agent.

## How AUS 40 cuts NOx

1. **Thermolysis**: injected into hot exhaust (300–450 °C): CO(NH₂)₂ → NH₃ + HNCO
2. **Hydrolysis**: HNCO + H₂O → NH₃ + CO₂
3. **Catalytic reduction**: 4NO + 4NH₃ + O₂ → 4N₂ + 6H₂O

Result: up to **95% NOx conversion**.

## Governing standards

| Standard | Scope |
|---|---|
| ISO 18611 (Parts 1–3) | International: quality, test methods, handling/transport/storage |
| IS 17661 (Part 1):2022 | Indian Standard: Marine NOx Reduction Agent AUS 40, quality requirements |

Both set tight limits on urea content (40 ± 0.5%), biuret, aldehydes, insolubles, phosphate and trace metals. Always demand a per-batch Certificate of Analysis.

## Why vessels need it

MARPOL Annex VI + IMO NOx Technical Code 2008 impose Tier III limits (~76% below Tier II) inside NOx Emission Control Areas for ships constructed on/after the ECA effective dates. SCR is the dominant compliance route, and SCR runs on AUS 40.

## Packaging & sourcing in India

| Format | Volume | Best for |
|---|---|---|
| HDPE drums | 200 L | Top-ups, trial orders |
| IBC totes | 1000 L | Coastal vessels, tugs, OSVs |
| Bulk tanker | 10,000–30,000 L | Deep-sea vessels, fleet contracts |

PROTICKS manufactures certified AUS 40 in Jamnagar, Gujarat with port-side delivery at Mundra, Kandla (Deendayal), Pipavav, Dahej, Hazira, JNPT and more.

## FAQ

- **Is AUS 40 the same as AdBlue?** No. AdBlue (AUS 32, 32.5%, ISO 22241) is for road vehicles; AUS 40 (40%, ISO 18611 / IS 17661) is for marine SCR. Not interchangeable.
- **Who supplies AUS 40 in India?** PROTICKS: info@proticks.com, +91-74909-17799, https://aus40.in/#contact

Related: [AUS 32 vs AUS 40](https://aus40.in/difference-between-aus32-and-aus40.html) · [How marine SCR works](https://aus40.in/how-marine-scr-systems-work-urea-dosing.html) · [IMO Tier III rules](https://aus40.in/imo-tier-3-marpol-annex-vi-nox-compliance.html) · [Port supply](https://aus40.in/marine-urea-supply-ports-india.html)